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052 The Cardiac Cycle

Ever wonder what happens in a heartbeat? What happens inside our heart when we hear the ‘lub-dub’ sound?

Watch and see as Leslie describes in full detail what a cardiac cycle is and how this is reflected in one heartbeat.

Have fun!

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun! My name is Leslie Samuel, and in this episode, Episode 52, I’m going to be talking about the ‘Cardiac Cycle.’ When I say the cardiac cycle, I’m talking about all of the events that happen with one complete heartbeat. So, we’re going to go into the details of this. There are a lot of details but, we’re going to try to break it down, one step at a time to make it as easy and as fun as possible. Let’s get right into it.

Here, we are looking at the entire cardiac cycle. We have this graph here that shows a number of details and, to make this as easy as possible, what we’re going to do is we’re going to take everything and break it down one section at a time. I want you to follow me on this. Like I said, we’re talking about one complete heartbeat and with one complete heartbeat, I’m talking about the contraction and the relaxation of the atria and the contraction and the relaxation of the ventricles. Anytime I say contraction, I’m referring to systole which is the CMS contraction; and, when I say relaxation, I am referring to diastole.

What we’re going to do is first, I’m going to describe what all these things show, and then, we’re going to take it one stage at a time.

Here, we’re looking at the phonocardiogram. In other words, we’re looking at the sounds that we hear when the heart beats, when we’re looking through the different stages of the heartbeat. Then, here we’re looking at the electrocardiogram, and we’ve looked at that in a previous episode. You can always revisit that to get a good understanding of how the electrocardiogram or the ECG or the EKG works.

Then, we’re looking at the ventricular volume. In other words, we’re looking at the amount of blood, the volume of blood in the ventricle, specifically we’re looking at the left ventricle. Then, here in blue, we are looking at ventricular pressure. So, that’s the pressure in the left ventricle. Here in gray, we’re looking at the atrial pressure, so, the pressure in the atria. Then, last but not least, we’re looking at the aortic pressure, and that’s the pressure in the aorta which is this structure right here, which sends the blood from the heart to the rest of the body.

That’s an overview of what we’re going to be looking at. Now, we’re going to take it one section at a time. This has a lot of details in it. It summarizes the entire cardiac cycle so, we’re going to take it one step at a time and get a good understanding of what is going on. Actually, I am going to start right in this section here. The reason I’m going to start here is because here we have showing the P, Q, R, S complex and the T wave. This is one full cycle but, this is labeled differently so, we’re going to look at that.

I’m going to start by looking at the electrocardiogram. First thing we’re going to see is we have the P wave, and if you remember from a previous episode, the P wave represents atrial depolarization. So, we’re talking about the depolarization of the atria. Once this happens, that is going to cause the atria to contract. So, let’s jump up here and look at the atrial pressure. You can see here, right after the P wave we get this increase in pressure in the atria. That is when the atria are contracting and that is why we see that increase in pressure as a result of the depolarization of the atria. Once again, the P wave represents atrial depolarization that is going to cause atrial contraction or, as you can see here, atrial systole. What that’s going to do is that’s going to push the last bit of blood from the atria, which is this part over here (I’ll show it with a blue pointer), from the atria into the ventricle. So, we’re going from the left atria, left atrium to the left ventricle when that contracts. That is why we see this quick increase in the amount of blood in the left ventricle. So, we get an increase in ventricular volume right after the atria contracts.

We’ve described this section here which is the atrial systole. And then, after the P wave, we then get the QRS complex. Once again, we’ve covered this in a previous episode, I think it’s Episode 48 where we talked about the EKG. The QRS complex represents the depolarization of the ventricles. And of course, once the ventricles depolarize, that’s going to cause the ventricles to start to contract just like after atrial depolarization, we get atrial contraction.

Now, after ventricular depolarization, we also get ventricular contraction. So, that is where we’re starting this phase of systole where the ventricles are contracting. However, there is a short period here, and you can see here the same period. It’s called isovolumic or isovolumetric contraction. That is when these valves, the atrioventricular valves and the semilunar valves are closed as there’s a buildup in pressure. You can see there’s a significant increase in pressure here during the stage of isovolumetric contraction. Of course, the volume of blood in the ventricles is staying the same. So, here, you see the left ventricular volume is staying the same. At a certain point, we will have enough pressure in the ventricle to cause the semi-lunar valve to open so that you can pump the blood into the aorta. Now, at what point is that? Well, you can see here the aortic pressure is somewhere around 80 mm Hg as you can see here. So, once we have enough pressure to overcome the pressure in the aorta, that’s going to cause the valve to open, and then the blood can be sent to the aorta which can then go to the rest of the body.

In the case of the ventricular volume, when those valves open, and the blood leaves, that’s going to cause the ventricular volume, the amount of blood in the ventricles, to decrease significantly. Why? Because the ventricles are contracting, we’re sending the blood out to the body so, that it can go to the muscles, the organs that need blood and oxygen, and all that good stuff. That is the result of the ventricles contracting, so you can see the increase in pressure, the blood being ejected so, you can see the decrease in ventricular volume, and that happens right after the QRS complex which is the depolarization of the ventricles.

So, thus far, we’ve looked at the P wave, atrial depolarization causing atrial systole or atrial contraction. Then, we’ve looked at the QRS complex which then causes ventricular contraction and increase in pressure. Here you have isovolumetric contraction where the valves are close and no blood is exiting the ventricles and then, you have the semilunar valves opening when the pressure in the ventricles can overcome the amount of pressure in the aorta, and that causes ventricular ejection. You can see the term here, ‘ejection’ that means that the blood is being ejected from the ventricles. You can see there’s a significant decrease in ventricular volume.

Then, we have this T wave that represents the repolarization of the ventricles. When the ventricles repolarize, that’s also going to cause the ventricles to relax so, you can see now the amount of pressure in the ventricle is going down significantly. Then, at a certain point, we didn’t talk about this in Episode 51 where we spoke about isovolumetric contraction, the same thing is going to happen on the opposite end where we have isovolumetric relaxation. And, that’s because the valves are closed, the pressure is decreasing, so, you’re going to get a significant drop in pressure while the volume of blood in the ventricle is staying constant. Then, once that’s done, the ventricles are relaxed, the atria are also relaxed the, we can get ventricular filling where blood is being sent back. You can see here during relaxation, this is where the filling happens, blood is coming back from the body, blood is coming back from the lungs and entering the ventricle, so the ventricular volume is going to start going up again, it’s going to increase as you see here, the full thing, increases until we get that P wave again which causes atrial depolarization, and the cycle continues.

Now, there’s one thing we didn’t look at as yet, and that’s the phonocardiogram. You can see here, we have a signal here, a signal here, a third signal here, and there’s actually even a fourth signal. What these represent would be the sounds of the heartbeat. When you listen to the heartbeat, you usually hear a ‘lub-dub’ sound: ‘lub-dub,’ ‘lub-dub,’ ‘lub-dub.’ What that refers to would be the first and the second sound that you see here. Yes, there’s a third sound and there is a fourth sound but, you don’t hear those because they’re not strong sounds. The two main sounds that you hear are the first and the second. What that refers to is the closing of these valves. So, at this point after the QRS complex where the ventricles depolarize and the ventricles start to contract, when they start to contract, that’s going to cause an increase in force closing the valve, closing this atrioventricular valve, and when that valve shuts, you’re going to hear that first sound, the ‘lub’ sound. Then, here, where the ventricles relax after sending all of that blood out, you’re going to get a closing of the semilunar valves and you’re going to hear the second sound which is the ‘dub’ sound. So, you get ‘lub-dub,’ ‘lub-dub,’ ‘lub-dub.’ That is the heartbeat that you hear. This third sound here is when the ventricles are being filled, and as the ventricles are being filled, there’s going to be some turbulence in there and that’s going to cause a third sound but, you don’t hear that as much because there are no valves that are closing or anything of that sort. It’s just blood that’s flowing. The fourth sound that there is represents the filling of the atria with blood. Of course, since the atria are significantly smaller than the ventricles, that sound is going to be even softer. So, you don’t even see it in this phonocardiogram.

This shows the entire cardiac cycle. I hope that now that we’ve gone through all of the details, this entire graph does not look as intimidating as it might have looked when we first started. You can always revisit some of the previous episodes. In Episode 48, we deal with the electrocardiogram, we talk about isovolumetric contraction in Episode 51, and there are a few other episodes covering other details involved in this process.

That’s all for this video. Of course, you can visit the website at Interactive-Biology.com for more Biology videos and other resources. That’s it for now, and I’ll see you on the next one.

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Leslie Samuel is the creator of Interactive Biology. His mission is to use this site to Make Biology fun for people all over the world.

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Leave An AWESOME Comment

229 Responses to “052 The Cardiac Cycle”

  1. hayder August 30, 2011 at 10:59 am #

    this vid make cardiac cycle very clear to me and can you post vid talking about cardiac arrhythmia and i will be grateful

    • Lrsamuel August 30, 2011 at 11:20 am #

      Unfortunately, I can’t. I’m focusing on making videos as I need them for my classes, so I can’t take anymore requests at the moment.

      • hayder August 30, 2011 at 3:30 pm #

        never mind,i appreciate that and all your vid are useful to me because i am in college of medicine

  2. InteractiveBiology October 9, 2011 at 10:29 am #

    @ArwA1992 Oh wow, that’s pretty cool. Glad it’s useful!

  3. kerrie337 October 18, 2011 at 2:49 pm #

    This was so helpful, cheers!

  4. rmcdaniel423 October 18, 2011 at 7:20 pm #

    Great video!
    Question: Aortic valve opens when contracting vent. pressure exceeds the resting diastolic pressure in the aorta (80mmHg). Pressure waves cross there. At the end of vent. syst., relaxing vent. pressure drops below chock-full-O-blood aortic pressure and the valve shuts as aortic blood presses against the cusps. Why are the pressure waves different there? Why is aortic pressure 100mmHg and vent. pressure 60mmHg? Why doesn’t the aortic valve close at 80mmHg?

  5. InteractiveBiology October 18, 2011 at 9:10 pm #

    All questions are answered in the Interactive Biology forums from now on. Go to the website in the description and then visit the forum. This is to make it as efficient as possible as we have multiple people over there to help answer questions.

    All the best

  6. InteractiveBiology October 18, 2011 at 9:14 pm #

    @kerrie337 Glad to know it helped. All the best!

  7. ne0rne October 19, 2011 at 5:28 am #

    awesome

  8. ToRnAdO0504563168 October 19, 2011 at 4:32 pm #

    you really made it fun not like our prof. in collage, keep up the nice work

  9. InteractiveBiology October 19, 2011 at 10:03 pm #

    @ToRnAdO0504563168 Thanks for the feedback. Glad you are enjoying it! Stay tuned for many more!

  10. miiigoreng October 30, 2011 at 10:32 am #

    THank YOU!!

  11. viju345 October 30, 2011 at 10:25 pm #

    Thanx alot…..
    Very helpfulll…..

  12. xty070 November 1, 2011 at 10:42 am #

    Thanks a lot

  13. Shieek3080 November 3, 2011 at 10:05 am #

    Thank you!

  14. combymanje123 November 17, 2011 at 5:00 pm #

    thank you so much for helping :D

  15. InteractiveBiology November 17, 2011 at 9:24 pm #

    @combymanje123 You’re welcome! PLease stay tuned because we have more Biology videos coming very soon!

  16. InteractiveBiology November 17, 2011 at 9:24 pm #

    @Shieek3080 You’re welcome. More biology videos coming soon!

  17. InteractiveBiology November 17, 2011 at 9:25 pm #

    @viju345 Glad you’re finding value in it. Visit our site for more fun Biology videos!

  18. InteractiveBiology November 17, 2011 at 9:25 pm #

    @miiigoreng You’re welcome! Stay tuned for more :)

  19. InteractiveBiology November 17, 2011 at 9:26 pm #

    @xty070 You’re very welcome! Stay tuned. New Biology videos will be uploaded soon!

  20. InteractiveBiology November 17, 2011 at 9:26 pm #

    You’re very welcome! Stay tuned. New Biology videos will be uploaded soon!

  21. InteractiveBiology November 17, 2011 at 9:26 pm #

    @ne0rne Thank you!

  22. MaficSun November 21, 2011 at 9:55 pm #

    Remember walking into class late with all this stuff written on the board. i was so lost… not anymore. thanks a bunch.

  23. InteractiveBiology November 22, 2011 at 6:31 am #

    @MaficSun You’re welcome! Stay tuned. We have more Biology videos to be uploaded very soon! :)

  24. InteractiveBiology November 22, 2011 at 6:31 am #

    You’re welcome! Stay tuned. We have more Biology videos to be uploaded very soon! :)

  25. Neopluto November 22, 2011 at 11:49 pm #

    A Little slow for my taste. Less intro, more info.

  26. InteractiveBiology November 23, 2011 at 9:01 am #

    @Neopluto We’ll see what we can do. :) Thanks for watching though! There are more videos you might want to watch from our Biology website. More will be uploaded so, please stay tuned!

  27. InteractiveBiology November 23, 2011 at 9:01 am #

    We’ll see what we can do. :) Thanks for watching though! There are more videos you might want to watch from our Biology website. More will be uploaded so, please stay tuned!

  28. WTF919ful December 5, 2011 at 3:20 am #

    Great job sir.. Please keep continuing your great work. God bless you..

  29. InteractiveBiology December 5, 2011 at 10:11 am #

    @WTF919ful Thank you and God bless you too :)

  30. InteractiveBiology December 5, 2011 at 10:11 am #

    Thank you and God bless you too :)

  31. jadsal92 December 31, 2011 at 3:40 am #

    Thank you Thank you Thank you :’)

  32. InteractiveBiology December 31, 2011 at 8:59 pm #

    @jadsal92 You’re welcome! Please stay tuned for more Biology videos to be uploaded very soon!

  33. InteractiveBiology December 31, 2011 at 8:59 pm #

    You’re welcome! Please stay tuned for more Biology videos to be uploaded very soon!

  34. MissTasha3 January 10, 2012 at 2:52 pm #

    Thanks leslie!

  35. AHM391 January 10, 2012 at 11:47 pm #

    شكراً

  36. xxTaKe2xx January 29, 2012 at 9:57 am #

    log duh log duh log duh xD

  37. MsRnwannabe February 1, 2012 at 2:37 pm #

    Thank you, thank you, thank you!!!!

  38. SbinZAlrash February 3, 2012 at 7:43 pm #

    U R AMAZING!!!!!!!!!!!!!

  39. hjsfhgxdgd February 11, 2012 at 11:52 am #

    This is awesome Thank you VERY much !!!

  40. Lenisse0105 February 12, 2012 at 3:19 pm #

    You really make biology fun. Excellent video! keep going on. Greetings from Dominican Rep.

  41. ChrisLeggettMusic February 27, 2012 at 8:22 am #

    Thank you for this awesome video on the cardiac cycle!! So much better than trying to get all this from a textbook, and the zooming/video overlays are really useful!

  42. ChrisLeggettMusic February 27, 2012 at 8:22 am #

    Thank you for this awesome video on the cardiac cycle!! So much better than trying to get all this from a textbook, and the zooming/video overlays are really useful!

  43. raphaTHEmaskweeka February 29, 2012 at 12:19 pm #

    Thank you so much!! soo helpful

  44. milyensu March 4, 2012 at 2:00 pm #

    thanks alot.

  45. MegaDreamOo March 10, 2012 at 8:46 am #

    man u r star !!!!

  46. MegaDreamOo March 10, 2012 at 8:46 am #

    man u r star !!!!

  47. megamind150 March 17, 2012 at 10:30 am #

    omg! omg! omg!…ur just too awesome!!..if u were my teacher then i definitely would top every exams:)..thanks a lot

  48. alimystro1 March 18, 2012 at 3:13 pm #

    why the black mouse cursor eh?

  49. Aku899 March 21, 2012 at 4:42 pm #

    This video gets to the point and is described clearly; did not over exaggerate or over complicate things either. I appreciate this video (and many other students) very much, thank you!

  50. Aku899 March 21, 2012 at 8:42 pm #

    This video gets to the point and is described clearly; did not over exaggerate or over complicate things either. I appreciate this video (and many other students) very much, thank you!

  51. SuperKay92 March 25, 2012 at 12:22 pm #

    Just saying,, the girls is HOT,, btw Thank You Very Much,,it helps,,, *whos the girl again?? Nvm

  52. SuperKay92 March 25, 2012 at 4:22 pm #

    Just saying,, the girls is HOT,, btw Thank You Very Much,,it helps,,, *whos the girl again?? Nvm

  53. dgostas1 March 26, 2012 at 12:13 pm #

    great video… lubdub!! lubdub!!

  54. dgostas1 March 26, 2012 at 12:13 pm #

    great video… lubdub!! lubdub!!

  55. dgostas1 March 26, 2012 at 4:13 pm #

    great video… lubdub!! lubdub!!

  56. sherab March 27, 2012 at 11:02 am #

    Hi, Leslie Samuel! i really really like your Episodes. it’s very helpful for me. actually i’m a Tibetan monk who is learing homan physiology at Emory university. and my english is not good. so your videos with lecture article help me to good understand what’s going on in the classes. your speech is very clear and more easier to follow. thank you very much. i will be your student who really like teacher as you.

  57. MsRachana77 April 2, 2012 at 1:01 am #

    superb !helped me a lot.Thanks a lot.

  58. MsRachana77 April 2, 2012 at 5:01 am #

    superb !helped me a lot.Thanks a lot.

  59. tonimak89 April 4, 2012 at 2:56 am #

    thankss

  60. tonimak89 April 4, 2012 at 6:56 am #

    thankss

  61. raypd April 4, 2012 at 11:52 pm #

    good stuff..

  62. raypd April 5, 2012 at 3:52 am #

    good stuff..

  63. krankguy11 April 6, 2012 at 1:55 am #

    Finally I got it. Thanks a lot IB. I’m subscribing 2 ur site right now

  64. krankguy11 April 6, 2012 at 5:55 am #

    Finally I got it. Thanks a lot IB. I’m subscribing 2 ur site right now

  65. marriam saleem April 8, 2012 at 11:07 am #

    thank u very much sir….

  66. marriam saleem April 8, 2012 at 11:07 am #

    thank u very much sir….

  67. Anonymous April 8, 2012 at 3:07 pm #

    thank u very much sir….

  68. marriam saleem April 8, 2012 at 3:07 pm #

    thank u very much sir….

  69. OuZhenheng April 10, 2012 at 10:03 am #

    thank you for your sharing

  70. OuZhenheng April 10, 2012 at 2:03 pm #

    thank you for your sharing

  71. mww7889 April 10, 2012 at 9:42 pm #

    I wish it was you I was paying thousands of dollars to teach me this, instead of an overeducated old man who has tenure and can’t be fired from his university. I learned more here than I have in the passed 3 lectures. Thanks!

  72. mww7889 April 11, 2012 at 1:42 am #

    I wish it was you I was paying thousands of dollars to teach me this, instead of an overeducated old man who has tenure and can’t be fired from his university. I learned more here than I have in the passed 3 lectures. Thanks!

  73. JMukhi April 24, 2012 at 11:17 am #

    Thanks a bunch !

  74. JMukhi April 24, 2012 at 3:17 pm #

    Thanks a bunch !

  75. cicinh0 May 2, 2012 at 11:54 am #

    Thank you very much! Your explanation of cardiac cycle is much better than both Guyten&Hall and Ganong. Helps me very much in my preparations for the physiology exam in medical school in Norway.

  76. cicinh0 May 2, 2012 at 11:54 am #

    Thank you very much! Your explanation of cardiac cycle is much better than both Guyten&Hall and Ganong. Helps me very much in my preparations for the physiology exam in medical school in Norway.

  77. 786slizza May 8, 2012 at 6:02 pm #

    im watching all your muscle and heart videos one day before my finals and i must say iv learnt more in these past two hours than i have in the past 4months!!!!! THANK YOU

  78. juman islam May 8, 2012 at 6:02 pm #

    im watching all your muscle and heart videos one day before my finals and i must say iv learnt more in these past two hours than i have in the past 4months!!!!! THANK YOU

  79. juman islam May 8, 2012 at 6:02 pm #

    im watching all your muscle and heart videos one day before my finals and i must say iv learnt more in these past two hours than i have in the past 4months!!!!! THANK YOU

  80. unloopy1 May 13, 2012 at 9:01 pm #

    Someone may already have made this point, but I notice that in the diagram here the pressure in the ventricle drops below that in the aorta well before the aortic valve closes. I think a corrected image is on wikipedia now.

  81. unloopy1 May 13, 2012 at 9:01 pm #

    Someone may already have made this point, but I notice that in the diagram here the pressure in the ventricle drops below that in the aorta well before the aortic valve closes. I think a corrected image is on wikipedia now.

  82. PhantomaticJack May 20, 2012 at 2:41 pm #

    A-Level Biology students with BY2 tomorrow say thanks!

  83. PhantomaticJack May 20, 2012 at 2:41 pm #

    A-Level Biology students with BY2 tomorrow say thanks!

  84. Fi007ful May 23, 2012 at 11:06 pm #

    Merci Beaucoup!

  85. Fi007ful May 23, 2012 at 11:06 pm #

    Merci Beaucoup!

  86. CuteYezidiGirl June 2, 2012 at 9:35 am #

    The best explanation ever!… Thumbs up for u man!

  87. CuteYezidiGirl June 2, 2012 at 9:35 am #

    The best explanation ever!… Thumbs up for u man!

  88. SuperMakhado June 2, 2012 at 5:00 pm #

    wow thank you hey, best explanation ever

  89. SuperMakhado June 2, 2012 at 5:00 pm #

    wow thank you hey, best explanation ever

  90. Kim June 3, 2012 at 6:36 pm #

    Thanks so much Leslie! I learnt so much on the cardiac cycle :D

  91. DonWisdom16 June 19, 2012 at 10:27 pm #

    Who else was perving on that woman at 11:04 LOOOOOOOOOOL

  92. DonWisdom16 June 19, 2012 at 10:27 pm #

    Who else was perving on that woman at 11:04 LOOOOOOOOOOL

  93. Devovanfleet June 24, 2012 at 10:49 pm #

    This was extremely helpful. I’ve watched it several times. THANK YOU!!!!!

  94. Devovanfleet June 24, 2012 at 10:49 pm #

    This was extremely helpful. I’ve watched it several times. THANK YOU!!!!!

  95. christaglo014 June 25, 2012 at 2:20 am #

    Thank you so much, you are a big help !

  96. christaglo014 June 25, 2012 at 2:20 am #

    Thank you so much, you are a big help !

  97. mariakiser June 30, 2012 at 10:50 pm #

    makes it crystal clear…you should be teaching at my college!

  98. mariakiser June 30, 2012 at 10:50 pm #

    makes it crystal clear…you should be teaching at my college!

  99. mariakiser June 30, 2012 at 10:50 pm #

    makes it crystal clear…you should be teaching at my college!

  100. YcDoc July 10, 2012 at 7:23 pm #

    Hi Leslie congratulations and thank you, I just discovered your videos, I was thinking that another way that you can help you to afford this effort is become a partner with google and youtube, and allow ads in your videos, with any click to the ads that you got you will receive some money. I know you are doing this for share and help but also you have to be compensate for your time because is the only way to make this nice effort sustainable.
    Thanks again and congratulations, i wish you success.

  101. YcDoc July 10, 2012 at 7:23 pm #

    Hi Leslie congratulations and thank you, I just discovered your videos, I was thinking that another way that you can help you to afford this effort is become a partner with google and youtube, and allow ads in your videos, with any click to the ads that you got you will receive some money. I know you are doing this for share and help but also you have to be compensate for your time because is the only way to make this nice effort sustainable.
    Thanks again and congratulations, i wish you success.

  102. just1nc89 July 24, 2012 at 2:45 am #

    great explanation

  103. just1nc89 July 24, 2012 at 2:45 am #

    great explanation

  104. vapi1893 September 6, 2012 at 8:05 pm #

    can you please post link for vector analysis ..i cant find it :/

  105. Lucy cortes September 16, 2012 at 3:18 am #

    Thank you for your time, you have a noble heart :)

  106. zorro vaughn September 23, 2012 at 9:00 pm #

    totally awesome and your voice is so smooth and easy to listen too, no jumping around , concise all the way through. WOW!!! is right , so glad I saw this and your other videos. Give yourself a you tube nobel prize.

  107. magicalair September 26, 2012 at 10:03 pm #

    I seriously love your videos! Thank you for doing this! You are such a great help to students and anyone who just wants to learn everywhere!

  108. Andrew Eng October 1, 2012 at 12:52 am #

    This is amazing! Thank you so much. :)

  109. tuanngo0990 October 4, 2012 at 7:08 pm #

    Hey, your website and your video are awesome. I m a visual learner, and your videos help me perfectly with A&P class. Thanks a lot!

  110. alejandrovaco1 October 7, 2012 at 3:10 am #

    Genial Leslie!, saludos desde el sur
    Great Leslie!, greetings from the south

  111. belieberdania October 7, 2012 at 9:15 pm #

    They is WAAY simpler than how my teacher explain. Thank you.

  112. Kelsey Rowan October 10, 2012 at 5:41 am #

    Thank you soooo much!!!! This helped clear up some confusion before my exam!

  113. ANM219 October 17, 2012 at 5:11 am #

    You are Amazing!!!!!

  114. rexexdesign October 17, 2012 at 7:01 am #

    Best video on cardiac cycle, hands down!

  115. Lucas Moura October 18, 2012 at 1:54 am #

    .k

  116. Sandika Samarakoon October 19, 2012 at 9:27 pm #

    Your such a great teacher,thanks a milloin :)

  117. Sandika Samarakoon October 19, 2012 at 9:28 pm #

    Your such a great teacher,thanks a million :)

  118. HEADSH0TSCOTT October 22, 2012 at 4:59 pm #

    I needed a quick refresher and this really helped. Best video I’ve seen on the subject.

  119. NaemaAhmad October 23, 2012 at 4:19 am #

    Awesome explanation, especially right before my midterm for A&P!!

  120. jjangjangz October 26, 2012 at 1:13 pm #

    thank you for the video!! I understood so much more from this than a two hour lesson from my teacher ;w;

  121. aerozenith208 October 31, 2012 at 6:18 pm #

    This video is great. Very detail!

  122. Darlene Naranjo November 1, 2012 at 2:42 am #

    I love your accent!!!!

  123. solstus November 4, 2012 at 4:29 pm #

    Are you Jamaican?
    I hear a hint of that in your accent.
    Anyway great videos and greetings from Jamaica!

  124. kae3126 November 7, 2012 at 4:30 pm #

    Thank you. great help! :)

  125. hesc2139 November 9, 2012 at 4:14 pm #

    No other video or college professor has been able to make this any more clear for me…and you did it in less than 14 minutes! I wish I would have found your videos earlier! This video makes the whole process so easy to understand. Your videos make an excellent reference. Thank you!

  126. mlittlej1 November 11, 2012 at 3:41 pm #

    These videos are amazing! Thank you!!!

  127. Brad Ogden November 11, 2012 at 3:45 pm #

    Fabulous video. You are a great teacher!!!

  128. Yordanos November 13, 2012 at 11:29 am #

    Thanks for your time may God bless u more.

  129. Mihir Shrestha November 13, 2012 at 6:10 pm #

    I learned more in this 13 min then i did in 3 hours of lessons.

  130. Chi Wai Lo November 20, 2012 at 4:47 am #

    I think your speed is great. It allows me time to digest the information. Great job!!

  131. Bushra Yasin November 20, 2012 at 5:51 am #

    thank you, you saved me. I wish my professor is as good as you :)

  132. 1860mc November 29, 2012 at 8:52 pm #

    I’m a bit stuck with polarization can anyone provide a link to an explanation please

  133. Midhat Khan December 7, 2012 at 5:40 pm #

    amazing teacher!!! thank you

  134. Rebemer4 December 8, 2012 at 12:55 am #

    Thank you so much!

  135. Nash Suelto December 11, 2012 at 9:08 pm #

    I just discovered your channel and it is so helpful! :D

  136. dianalefm December 14, 2012 at 9:24 pm #

    Magic!

  137. elgonzobonzo December 20, 2012 at 10:46 pm #

    Congratulations and thank you very much for sharing all these videos. You make something complex very simple and clear !!! Some people said that it is a little bit slow, but for me it has the right speed to make it comprehensible. Thanks again !!!

  138. Prettyspeck December 21, 2012 at 8:30 am #

    This is amazing!

  139. Chris D'Almeida January 1, 2013 at 11:05 pm #

    Thanks for the video :) 5* I’ve got an exam on the 9th of January 2013 and though a video could help! Will be visiting your website and may tell my friends about it! Thanks again

  140. khuniswayyybetter January 6, 2013 at 9:03 am #

    your channel is amazing!!
    thank you and much respect

  141. Alice Gray January 10, 2013 at 10:31 pm #

    This is amazing, thank you so much, might just make it through my exams now!

  142. Tabitha Taylor January 21, 2013 at 9:13 pm #

    what do the “c” and “v” waves on the atrial pressure wave indicate?

  143. jozifmm January 25, 2013 at 8:42 pm #

    You’re videos are extremely helpful! Thank you so much!!

  144. z hanim January 31, 2013 at 2:42 pm #

    my friend told me about your videos and these are awesomes!! thanks a lot :)

  145. zeinab galal February 8, 2013 at 9:01 am #

    c wave is due to rise in the atrial pressure produced by sudden closure and bulging of the tricuspid valve into the atria during isometric ventricular contraction , while v wave is due to rise in the atrial pressure as well but here due to accumulation of the venous return while the AV valves r closed , that’s all i know :D

  146. Katie Pritchett February 13, 2013 at 5:14 am #

    I just came.

  147. Splinter4077 February 15, 2013 at 2:47 am #

    My heart has gone through so many rhythms since watching this video. Makes you think a little!

  148. S1mpleStepz February 18, 2013 at 7:44 am #

    man i swear this man Leslie Samuel deserves an award

  149. hockey724 February 21, 2013 at 11:25 pm #

    Leslie Samuel is god

  150. nabil barsoom February 23, 2013 at 10:53 am #

    thank u indeed , an easy and simple way of teaching , but wishing a richer scientific subject .

  151. chakradhar sams February 24, 2013 at 2:08 pm #

    Thanks, a Lot Samuel. Kui very Nice. I had neuer unterstand that diagram but now ist cristall clear. Thanks

  152. mimi mj March 4, 2013 at 9:20 pm #

    I have a similar diagram in my book as was beyond confused in trying to make sense of it and understand how all the different parts correlate with each other. This video was absolutely amazing at describing each little part, and it put everything together like a story. Very thorough and helpful!!

  153. nedybuny March 5, 2013 at 9:48 am #

    Thank uuuuuuuuu:)

  154. 703411 March 12, 2013 at 9:36 pm #

    Im in nursing school and i couldnt understand this and I was soo stressed. But now i get it finally…I want to thank you!!!!!!!!! YOU HAVE NOOO IDEA HOW MUCH THIS HELPED ! KEEP IT UP :))))

  155. Tamarc3 March 13, 2013 at 6:17 pm #

    You are absolutely amazing!! Can’t thank you enough

  156. Latasha Turner March 15, 2013 at 6:03 pm #

    Thank you from the bottom of my heart! (corny pun intended) :-)

  157. MMM2345DDD March 15, 2013 at 9:34 pm #

    I just discovered your channel. Great presentation with easy to absorb descriptions and instructional materials. I shall explore your other videos. Thank You!

  158. Marcela Martinez March 15, 2013 at 11:34 pm #

    I want to punch my professor -_- He gives me headaches!. You rock!!!!!.

  159. Jen Livingston March 18, 2013 at 11:52 pm #

    Thank you!!!!! :D

  160. Trang Cao March 24, 2013 at 9:52 pm #

    I just got a decent grade in my last anaotmy exam! Thanks soo much to this channel !!! I have another exam comming up and this vid is awsome!

  161. Ayesha I March 25, 2013 at 10:51 pm #

    Sir, you are AMAZING!!! Thank you for making this very easy and fun to understand!!

  162. Amelia Stephenson March 26, 2013 at 12:11 pm #

    Come teach physiology at my school!!

  163. Patrick Wilkinson March 30, 2013 at 1:19 pm #

    Thank you for such informative, and easy to understand videos. You really do a wonderful job. Keep it up.

  164. Missprak April 3, 2013 at 10:46 am #

    Excellent teaching of the Cardiac cycle, may God continue to bless you with your great generosity

  165. volumelow April 8, 2013 at 1:52 pm #

    Universities should replace all professors with these youtube personnel (people who actually enjoy teaching and speak proper English).

  166. BibliaInspirada April 9, 2013 at 11:01 am #

    Comer pan negro, cereales integrales, frutas y lechuga. La leche de vaca es peligrosa. Tener alegria, habitos positivos y menos estres, enfrentar los problemas con esperanza y optimismo. No consumir grasa animal como la crema, helado de crema, etc. Recomiendo no fumar no tomar alcohol. La depresion hace mal, debemos buscar buen apoyo. Si se puede, realizar ejercicio aerobico. Llevar una vida espiritual y tener un caracter manso. Tomar mas agua conservando la moderacion en todo:.

  167. Saima Zaki April 11, 2013 at 7:04 am #

    Awesome, very clear and understandable language. It will helpful for me for my tomorrow physiology test. I learn much more in this 13 min than my hoursssssssss study.
    Thank you, love it.

  168. Burnin' Helen April 12, 2013 at 1:06 pm #

    Thank you SO MUCH for these videos, I have a particularly inconsistent and confusing teacher for physiology who is unable to organize the material in a way that makes sense and is cohesive. I wish I could have paid you the tuition instead as these videos are how I am really learning. I wish all teachers could teach the way you do. you are amazing! Truly, from the bottom of my heart, thank you!

  169. BiL0Logy April 15, 2013 at 6:44 am #

    Great video, by the way it’s pronounced systole, like lamp pole. Not systoly

  170. Praew Chinsomboon April 16, 2013 at 12:40 pm #

    I would to thanks you for contributing time and efforts to make this video! A+++ Awesome! You are much better than my professor, who should learn more of how to teach! Not just speak!!

  171. Praew Chinsomboon April 16, 2013 at 12:40 pm #

    I would to thanks you for contributing time and efforts to make this video! A+++ Awesome! You are much better than my professor, who should learn more of how to teach! Not just speak!!

  172. Jo L April 17, 2013 at 2:47 pm #

    No, it’s not. He’s pronouncing it right.

  173. alphabeta71113 April 18, 2013 at 6:04 pm #

    Mulahemum YOUR AWESOME!!!!!!

  174. TheIlovetequilla1 April 22, 2013 at 10:57 am #

    Why does atrial pressure rise slightly during systole? Answer anyone?

  175. Areen Ghazi April 23, 2013 at 8:43 am #

    because it contracts thus increasing the pressure within it,,and of course it will not contract as much as the ventricle contraction ( the blood will pass from the atrium to the ventricle below it,,so we don’t need a huge pressure to do that, bearing in mind that the flow of blood will pass passively at first depending on the pressure gradient only),,if you are asking about why does it increase in the ventricle systole,that is because the AV valves bulge into the atria…good luck :)

  176. Nigel Karu April 25, 2013 at 2:23 am #

    100% agree

  177. TheIlovetequilla1 April 25, 2013 at 12:14 pm #

    Thank you :)

  178. TheIlovetequilla1 April 25, 2013 at 12:22 pm #

    Also i love the way you say p wave! Your voice is amazing lol!

  179. Peter Kim April 29, 2013 at 8:18 pm #

    THANK YOU :D

  180. Hugh Bassett May 2, 2013 at 7:33 am #

    Thanks, this was very helpful.

  181. MrTolly May 12, 2013 at 5:04 pm #

    This is even better with automatic captions on, haha

  182. Franssi AL May 13, 2013 at 4:39 pm #

    GREAT GREAT, THANKS <3

  183. BlimeyGeezaMate May 20, 2013 at 6:12 pm #

    Am I the only person who sees a big blue penis on the right heart?

  184. Liliana Lopez May 21, 2013 at 9:44 pm #

    GREAT!

  185. Dearhaz May 28, 2013 at 6:43 pm #

    Thank you for this great video, I got an A in the lecture exam.

  186. fred highday June 5, 2013 at 9:41 pm #

    What a incredible explanation..2 thumb

  187. malak dahan June 8, 2013 at 3:49 am #

    i had never understand the cardiac cycle and how it works but now its diffrent i really wanna thank u

  188. malak dahan June 8, 2013 at 3:50 am #

    thnx alot

  189. Solomon Angom June 14, 2013 at 6:11 am #

    Thank You Internet!

  190. Michell Lopez July 7, 2013 at 9:34 am #

    Excellent!

  191. GiaVonni Virella July 9, 2013 at 10:20 pm #

    I’ve found my new bestie!!!! Hello A. Thank you Sam. So clear, so concise, so simple.

  192. tsangarisjohn July 13, 2013 at 3:49 pm #

    Thank you?, very well executed!

  193. Sartorius988 July 26, 2013 at 4:48 pm #

    I’m just wondering, when the ventricles are contracting and the aortic value is open, aka when the ventricular volume is dropping, are the atria filling up with blood?

  194. Sartorius988 July 26, 2013 at 4:48 pm #

    I’m just wondering, when the ventricles are contracting and the aortic value is open, aka when the ventricular volume is dropping, are the atria filling up with blood?

  195. chucky362 August 10, 2013 at 12:43 am #

    Who ever gave this a thumbs down should go kill themselves

  196. Zaid Zikri August 15, 2013 at 8:43 pm #

    16 people,never went full retard.

  197. kerry August 23, 2013 at 8:46 am #

    I will love to have access to your program

  198. sam aryan August 30, 2013 at 3:01 pm #

    Hi mr.samuel
    these 3 questions have baffled me for a while,
    Q1:when exactly dose the sodium-potassium pump’s job start?
    1 right after the hyperpolarization 2 as soon as the cell reaches the resting state
    if the assumption #2 is correct then in that case the hyperpolarization is sending K+ out while the pump is pumping K+ in?? is’nt it contradictory or maybe the assumption #1 is correct.
    (plese check out my next comment because youtube doesnt let me to post it all in one comment)

  199. sam aryan August 30, 2013 at 3:02 pm #

    Q2:IS refactory period the same as the activity of sodium-potassium pump? if the assumption 1 is correct then it can not be said that all that part of the graph which is under the line of resting state is all”refractory state”
    Q3:why the Q and S in ORS complex are under hre isoelectric line?and which one causes the U wave, the depolarization of the purkinje fibers or repolarization of them
    I would mean a lot if you take your time answering my question,thanks….

  200. IDr. Scientist September 7, 2013 at 7:59 am #

    I love you … Thank you very much

  201. tmoore15wvu September 12, 2013 at 6:03 pm #

    I am now One Happy Med Student!!!

  202. wooohooooo September 15, 2013 at 7:04 am #

    Thanks so much. I go to one of the best schools in UK but I understood better with this vid.

  203. Jaroli September 22, 2013 at 11:32 pm #

    Why does the QRS wave go below the baseline? I am confused about what the axes of the graph are representing. What is on the y axis? Is going above the baseline becoming more positive? Or is it measuring volts or something of the like? Please help this poor confused student!

  204. Ilhan Ali October 6, 2013 at 6:06 pm #

    Hi, why is the volume in the ventricles increasing before you reach the Pwave? Is there blood entering the ventricles BEFORE the atria contract?

  205. thegarbageman21 October 7, 2013 at 11:28 pm #

    Yes you are correct. The ventricle AV valves are open and at ventricular low pressure (after relaxation) so the blood will pour in from the atria. Remember you have all that blood coming into the atria from the Vena Cava which makes atria have more pressure than vent. In young people ventricles actually get over 80% of the blood before the atria contract. When you get older however the ventricles get stiffer so that atrial pumping mechanism becomes more important to squeeze that blood in.

  206. Canpean Ionut October 12, 2013 at 6:02 pm #

    I can’t say anything more than: “Respect.” . I do respect this man for what he is doing and I think we all should.

  207. lavokr October 14, 2013 at 8:25 pm #

    Thanks for the video! Very helpful :D

  208. Rupinder Nahal October 18, 2013 at 10:55 am #

    Life saver! :))

  209. Rebeka Fastnedge October 22, 2013 at 3:42 am #

    I love you!

  210. Jennifer Chen October 22, 2013 at 8:49 am #

    Hey, from what I know, after the atria filling (isovolumetric relaxation), the pressure rises in atria causing the AV valves to open and blood starts filling the ventricles. THEN the atria depolarizes and contracts finish filling the ventricle (sort of like topping it off)

  211. EireneHarmonia October 27, 2013 at 6:16 pm #

    Thank you so much.

  212. marijaunnaz October 30, 2013 at 5:37 pm #

    Haha, WIGGER

  213. marijaunnaz October 30, 2013 at 5:37 pm #

    Haha, WIGGER

  214. Asmah Emmanuel November 3, 2013 at 1:10 am #

    i wonder why some people will unlike this.

  215. Awdaly Saleh November 3, 2013 at 3:15 pm #

    Thank you .

  216. TheKimber0615 November 4, 2013 at 10:02 am #

    What word that was used is not considered english. Maybe you should teach people. Judging those who help, why?

  217. Debster675 November 5, 2013 at 2:00 am #

    I’ve learned more from you in just one video than I have from a human physiology class in a four year university. Thank you soo much! :D

  218. DJrockSStar November 5, 2013 at 12:49 pm #

    Thnx man !

  219. yarob zedan November 7, 2013 at 7:17 am #

    Amazing Vedio.. it’s really helpful !!

  220. Courtney Westbrook November 7, 2013 at 10:41 pm #

    Hey, Leslie. I’m a senior in college and am in Animal Physiology this
    semester and it’s killing me! Thank you so much for taking the time to post
    all these videos. They are so helpful!! I just wish I had discovered these
    earlier and I’d probably have an A and not a B! :)

  221. Ben Ochoa November 10, 2013 at 12:24 pm #

    I love this!! Can I jump on this band wagon and help out???

  222. TatamiMusician November 12, 2013 at 2:57 am #

    Lub dub, lub dub! :D Thank you very much! This has been very helpful! :)

  223. banandababa November 16, 2013 at 10:01 am #

    YOU ARE AMAZING ! i get it now :)

  224. zachariahm10 November 19, 2013 at 5:19 pm #

    thank god for this

  225. M.B January 19, 2014 at 7:54 pm #

    You explain things much more clearly than university lecturers in the UK! Thank you :)

  226. Mbizzle January 20, 2014 at 7:55 am #

    I owe you my degree! Thank you :)

  227. Monica Merino March 23, 2014 at 5:02 pm #

    Amazing. Thank you!