Have you seen an ECG reading? What do those lines mean? How does it measure heart activity?
In this article, I’m going to show you how to read an electrocardiogram. For short, “electrocardiogram” is called ECG or EKG.
So, let’s get right into it. First, I want to answer the question…
What is an Electrocardiogram (ECG / EKG)?
An electrocardiogram (ECG/EKG) is a test that records the electrical activity of the heart. We looked at how the SA node starts the signal and we looked at how that signal spreads to the rest of the heart. You can always go back to this article for more details on how that works.
The ECG is used to test for irregularities in how the heart functions. You’ve probably either seen this first hand in a hospital or on TV. You can look at the electrocardiogram and it will tell you if the heart is working the way it should. The way this is conducted is by placing skin electrodes on different parts of the body.
These electrodes are able to detect the electrical activity of the heart. When you look at the electrocardiogram, it looks kind of like this and you’ve probably seen this.

Normally when you see this, there’s a beep associated with it (with the machine) but, you get the point. What we’re going to do is we’re going to look at this and we’re going to look at each component of the electrocardiogram.
ECG Waveform Explained
We’re looking at an electrocardiogram and you can see that we have a number of things. We have this peak over here. We’re going to call this the P wave, this peak right here. And then, we have this section that we’re going to call the QRS complex. Then, we have the T wave and sometimes we get this U wave. We’re going to talk about what these different waves show.

P Wave
The P wave. We’ve looked at how the SA node generates the signal and then that signal spreads to the muscle cells in the atria.
What this P wave shows us is the depolarization of the atria. So, when the atria depolarizes, we see this peak.
QRS Complex
We have the QRS complex, you probably guessed it by now. The QRS complex represents the depolarization of the ventricles.
T Wave
Then, we have the T-wave which comes after the QRS complex and this shows the repolarization of the ventricles.
Now, you’re probably wondering why the signals that come from the ventricles are significantly larger than this little signal that comes from the atria. But, if you look at the heart, you’ll see that the atria is significantly smaller than the ventricles. So, when the cells in the ventricles depolarize, that’s going to have a much greater effect on the EKG or the ECG because you have more cells depolarizing so you can get a stronger signal.
U Wave | Repolozarization
And then, of course, you get the repolarization. The U wave is one that you don’t always see. It’s sometimes hard to see and in most cases, you don’t really see it. But, in some cases, you do see it. In some cases, it can tell you something about when things are going wrong with the heart. We’re not going to go into all those details but, I included it here because it does show up sometimes.
Some people think it’s the repolarization of the Purkinje fibers. And it’s also thought to be the repolarization of some other specialized muscle cells. But, we’re not going to go into that.
The main things are the P wave, the QRS complex, and the T wave. The P wave being the depolarization of the atria; the QRS complex being the depolarization of the ventricles and; the T wave being the repolarization of the ventricles.
If you ever need a refresher on what the terms depolarization and repolarization mean, you can always go back to these articles:
Those articles will give you more details.
Sir,
The information in the video,although very useful seemed to be insufficient..SO, I would request you to make another video regarding abnormailities in each of the EKG waves..I would be thankful If you would give information about the same
Yours truly
Nikhil N T
Sir,
The information in this video was very useful. But, I wanted a bit more details ..If you would provide information about the abnormalities in each of these waves,it would be very helpful.
Yours truly
Nikhil N T
There’s always more information that can be added. However, there’s only so much that 1 person can cover. I try to give as much detail as I have. You can always do your own studies by reading textbooks that go into the level of detail you are trying to get.
Thank you so much for these videos.
@maihot You are very much welcome!
thank you very much
@yassomatto You are very much welcome 🙂
hey thanks for the video. I just had a ECG for the Canadian Army and the results says : ALMOST NORMAL. After viewing your video i came to the conclusion that….nah..all seems to check out OK…..with my untrained eyes 🙂 Awaiting the final results
@rotorway133 I wouldn’t use my video for self-diagnosis 😉 but I hope that all goes well with the results.
Excellent video!! Thanks for sharing. 🙂
Excellent video!! Thanks for sharing. 🙂
@MedAsstVera You are very much welcome 🙂
Awesome video, it’s explained really well but I just wondering when the atria repolarise, does it have a peak or is it too insignificant to see?
All questions are answered in the Interactive Biology community forums from now on. This is to make it as efficient as possible as we have multiple people over there to help answer questions.
All the best
what abt atrial repolarisation?
@missgomes18 All questions are answered in the Interactive Biology community forums from now on. Go to the website in the description and then visit the community. This is to make it as efficient as possible as we have multiple people over there to help answer questions.
All the best
@missgomes18 Atrial repolarisations are so small that they get masked on the ECG by the depolarisation of the ventricles (i.e. QRS complex).
this is awesome
@chas21969 Thank You!
i m a army doc
n i find it vry helpful as i m on a isolated place
thnxs
@jaaz1802 Glad to know the videos can help you from so far away. Thanks for the work You’re doing. It makes a difference!
why is the T wave “positive”? I understand, and it makes sense that the depolarization in the atriums and the ventricles have that effect on the EKG but not why the T wave is positive.
Thank you for great videos, I just found your channel and i love it!
why is the T wave “positive”? I understand, and it makes sense that the depolarization in the atriums and the ventricles have that effect on the EKG but not why the T wave is positive.
Thank you for great videos, I just found your channel and i love it!
This is fantastic!!! I am learning so much
This is fantastic!!! I am learning so much
@hannasspawnofsatan Glad you found some value in it. You can check our website for more. Do stay tuned because we’re planning to upload new Biology videos very soon!
Glad you found some value in it. You can check our website for more. Do stay tuned because we’re planning to upload new Biology videos very soon!
thanks this helped
thanks this helped
@VidUploDer You’re welcome! Stay tuned for more Biology videos coming very soon!
You’re welcome! Stay tuned for more Biology videos coming very soon!
thank you … i have been having problems with ECG but now i get it perfectly ..thanks to you
@akshalabi You’re welcome. Glad to know this helped. Stay tuned! We have more Biology videos coming very soon…
You’re welcome. Glad to know this helped. Stay tuned! We have more Biology videos coming very soon…
Excellent 🙂
Excellent 🙂
@biomed29 Thank you! Please stay tuned for more Biology videos coming soon!
Thank you! Please stay tuned for more Biology videos coming soon!
I don’t understand what depolarization and repolarization is?
please your opinion about:
“It mean’s a lot for me”
youtube.com/watch?feature=player_embedded&v=TKAL0YSDHIs
On
[email protected]
please your opinion about: “It mean’s a lot for me”
youtube.com/watch?feature=player_embedded&v=TKAL0YSDHIs On
[email protected]
thank you until now i didnt know about the u wave this helped a lot
@DiyaBabyee Interactive biology made videos about depolarization and repolarization, check them out.. ther’re pretty good
There is also a video about action potential it will help as well
Interactive biology made videos about depolarization and repolarization, check them out.. ther’re pretty good
There is also a video about action potential it will help as well
this helped so much thank you
where is more information on reading EKG’S AND INVERTED P WAVES AND inverted T waves.. Also some additional info to focus on mi detections and the contrast to people with pacemakers abd defibs ekg readings ..
so far I am enjoying your videos ..
I don’t have all that info here. There’s only so much I can do. There’s ALWAYS more that can be covered.
Glad you are enjoying the videos though.
Great video! You just didn’t explain that the QRS complex mask the repolarisation of the atrium (we can see on the edge of the QRS complex that the curve goes down a little) Thanks a lot for your videos anyway! It helped me a lot! 🙂
Great video! You just didn’t explain that the QRS complex mask the repolarisation of the atrium (we can see on the edge of the QRS complex that the curve goes down a little) Thanks a lot for your videos anyway! It helped me a lot! 🙂
so what part the atrium and ventricles contract and relaxed during depo and repo?
You don’t see the repolarization of the atria because it is overshadowed by the depolarization of the ventricles.
Thank you.
Thank you.
A pleasingly ratnaiol answer. Good to hear from you.
Thank you, this has been very helpful.
Thank you, this has been very helpful.
ahaha I’m an ECG TECH and looool it helps lol 😀
You sound Trini….good explanation! Thanks so much 🙂
thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you
thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you
thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you
Can anyone explain why P,R,T have a positive deflection, and Q,S have a negative deflection? I don’t understand why this is.
Can anyone explain why P,R,T have a positive deflection, and Q,S have a negative deflection? I don’t understand why this is.
Is there a video that show when SA node and AV node fire, when atria relax, when the ventricle relax, when valves open and close, and the points where ventricle pressure and volume is high or low? I really need help with that.
Is there a video that show when SA node and AV node fire, when atria relax, when the ventricle relax, when valves open and close, and the points where ventricle pressure and volume is high or low? I really need help with that.
Nice I like this link, it helps me to realize everything that I studied for EKG .. thank you very much 🙂
Good one. Thanks.
Good one. Thanks.
too basic, but well done
too basic, but well done
thank you very much. very good video and article. clear voice and easier to understand.
Hi my greatest teacher Leslie Samuel!
Actually i’m a Tibetan monk who are studying human physiology at Emory university. and this is my second year, i just learned english for one year before i came to here. so my english is so bad and always get language problem in my classes. recently i found your TVs and articles which very clear and more easy to understand to me. then i got really happy. now i watch your videos and read your articles which relevant my classes before i go to the classes. it help me to understand what’s going no in the classes. thank you very much.
sherab.
you are a great teacher! I can’t wait to take my test in school. thank you
you are a great teacher! I can’t wait to take my test in school. thank you
you are a great teacher! I can’t wait to take my test in school. thank you
you are a great teacher! I can’t wait to take my test in school. thank you
Thank You. This explanation is fantastic. Do you mind if I use this video to show patients in my Cardiology clinic? I would greatly appreciate it. Please advise. Thank You in advance.
Yes, you can do so. Thank you for using our videos. We hope your patients will find them useful and easy to understand.
Thank You. This explanation is fantastic. Do you mind if I use this video to show patients in my Cardiology clinic? I would greatly appreciate it. Please advise. Thank You in advance.
Yes, you can do so. Thank you for using our videos. We hope your patients will find them useful and easy to understand.
this helped me a lots.
this helped me a lots.
Great teaching … thanks Leslie
Great teaching … thanks Leslie
Muy bien !!
excellent!!!! i hd alot a problems regrading Ecg reading!!! but thanks to this video 🙂
excellent!!!! i hd alot a problems regrading Ecg reading!!! but thanks to this video 🙂
excellent!!!! i hd alot a problems regrading Ecg reading!!! but thanks to this video 🙂
thank you man, really helped a lot.
Done A Great Job/………………
thank you man, really helped a lot.
Done A Great Job/………………
Done A Great Job/………………
Done A Great Job/………………
Wow great lecture
Wow great lecture
Wow great lecture
this is really helping thank you!
this is really helping thank you!
this is really helping thank you!
You are the man! Thank you loads Leslie…
You are the man! Thank you loads Leslie…
Lessley you have succeeded in making this site the best available biology resource in the whole world wide web and I mean it. I am preparing for an Axam in the next 2 hrs and you have no idea how much your lectures are helping me right now. Thank you for being a greater person having others in mind and not just your self.
May God bless you for this
You are so very much welcome. Glad to hear the videos are helping you!
Great video – I’m doing my Para degree at the mo!
Great video – I’m doing my Para degree at the mo!
so where’s the repolarization of the atria? does it appear on the ECG?
so where’s the repolarization of the atria? does it appear on the ECG?
Atrial repolarisation is submerged within the much bigger QRS complex.
Atrial repolarisation is submerged within the much bigger QRS complex.
thank you !
thank you !
@ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx
@ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx
@ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx
I’m currently studying Cardio MedSurg in my nursing course and i was wondering could you make a video showing what the heart looks like when its in the different kinds of dysrhythmias? Its something i would be able to understand better if i can see how the heart beats during each kind. If you cant do you know where i can find a video like this?
I’m currently studying Cardio MedSurg in my nursing course and i was wondering could you make a video showing what the heart looks like when its in the different kinds of dysrhythmias? Its something i would be able to understand better if i can see how the heart beats during each kind. If you cant do you know where i can find a video like this?
What software and hardware do you use to make these videos? I’m about to go into medical school and I think it would be great if I could make videos as I go through school as a resource for people that follow behind me.
If you could help me to learn the software – and I am able to make the videos without legal restrictions (or time restrictions), I would allow you to host a copy of the videos.
Thanks!
Everyone is wondering – I just found the answer:
“You might be surprised that ventricular depolarization (the QRS wave) and repolarization (the T wave) point in the same direction, although they are produced by opposite potential changes. This is because depolarization of the ventricles occurs from endocardium to epicardium, whereas repolarization spreads in the opposite directoin, from epicardium to endocardium.”
Source: Human Physiology, By Stuart Ira Fox, Twelfth edition (copyright 2011) page 424
Hi Mike, I did a podcast episode about how I make my videos. You can check it out here.
allow me… 🙂
thanx(i downloaded it 🙂 )
allow me… 🙂
thanx(i downloaded it 🙂 )
allow me… 🙂
thanx(i downloaded it 🙂 )
what is a borderline ecg
Thanks!
Thank you sire! I am gonna download this….;)…i did have problem in ecg interpretation a bit now cleared….but still wanna keep this video as a rememberance….and revision point for exams…thanks once again…
Thank you so much !
awesome! wish Doctors here were like you. 🙂 most of them here get offended if I even ask them what they understood and what they think they will do to combat the problem. 🙂
thanks interactivebiology!.. the place where I live.. Doctors (most of them – actually every doctor I have met) do get offended if I even ask them what they are doing to combat a problem based on these readings..
i think i love you! you are my hero! 🙂 please keep the videos coming!!!
usless shit
interesting!
am looking to be trained as an ekg tech. this helped.
this is incredible. i have a test paper at medicine tomorrow and this video made the thing a lot easier
Outstanding. I sat through a two hour lecture and I was more confused than when I came in. This is straight to the point and very clear. Thanks.
One word. Incredible.
Awesome video!! Great way of breaking down the information it really helps.
It can be recognised not by using conventional ECGs but during some specialised electro physiology tests when both the atrial and ventricular waves are separated
Love this thanks for posting the video. I’m going into emergency medicine and this helps me understand EKG PQRST waves a lot better then what I learned in class!
I’m currently in pharmacy school and every one of your heart videos has helped me more than the lectures of my professors. thanks!
Extremely helpful thank you so much 🙂
Very nice explanation (need some drilldown to medical topics)
Hey Leslie, amazing video ! I’m not a Biology enthusiast (by the way, I’m an engineer), but you got my attention during all the explanation… You were born to teach and help others to understand things !! Keep it up man !! Congrats !
so thanks of you…. am not a doctor but an engineer … for my project sake i just cme across this ….. very crisp and clear
This Chanel always saves me. Thank you!!!!
this was great!
Your videos are quite helpful. Can you please explain the terms depolarization and repolarization in simple words?
see episode 9 or 10. 🙂
Thank you so much! This video was great and supper easy to understand ;my book was confusing me.
I enjoyed #048 how to read ECG. But could you do another video in more detail. I like how you teach and I would like to become better at reading the ECG. Maybe like a video for 10mins or so all about ECG/EKG..thank you again for all your videos!!
Thank you! Fantastic teaching – clear and to the point.
thank u
Thank you…
Thank you for the interest and helpful video
Thank You so much….I have read and reread this chapter. You made it make sense.
SI SOS MEDICO O ESTUDIANTE DE LA SALUD!! NO TE PODES PERDER EN MI CANAL
DALE ME GUSTA Y SUSCRIBITE PARA RECIBIR LOS VIDEOS Y MEJORE EL CANAL! NO TE PIERDAS LOS ULTIMOS VIDEOS DE EJE HEXAXIAL EN ECG
this vidio help me more………thank you and i with for you the best
I have hard time learning to figure out the heart rate by the rule of 300 of ECG , is there anyway you upload video show me the easy way to learn.
I thought U wave was indicative of hypokalemia.
fantastic!!
i’ll use it in my school conference
Interactive biology: are you the instructor for Jefrench?
thank you for this video. this will help my wife in getting her ACLS cert.
Thank you for your video! I’m a nursing student and appreciate your eagerness to share your knowledge.
spanish please!!!
brilliant thank you so, clean and simple to understand
I would to say thanks .You been helping me out so much is my classes.keep up the good work lol
When does the Atria repolarize>??
During the depolarization of the ventricles. Due to the large signal the ventricles send out, you just can’t see it 🙂
I love this guy’s videos. They help me a lot when I study for my A&P exams.
Thank you so much for these videos, they are such a huge help!
I love these videos! Thank you so much for taking your time to teach. They are so helpful and explain things that the instructors are not in class!
Thank You.
Awesome!
how to calculate the p wave altitude?
sam is hot.
during the QRS complex. which is why you don’t see a wave for it. (If I’m not wrong,what I got from lecture) .
Another simple let great video.
Remember AVDA
A- Atrial systole (depolarisation of atria/contraction of atria/P)
V-Ventricular Systole (depolarisation of the ventricles/contraction of the ventricles/P)
D-Diastole (repolarisation of the ventricles/relaxation of both atria and venticles/QRS complex)
A– Atrial systole (depolarisation of atria/contraction of atria/P)-ommiting U
Correct me if I’m wrong or thumbs me up for others to see.
Thank God a man that speaks english and knows more than my college teacher. Daymar College EKG class is awful because of the teacher. I’ve learned more on these videos than the teachings at the school. Thank you!
Hey man, are you guyanese?
another great video! I learn more from this than actual lecture in class…(=^D
thank you soooooo much!!!!
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thank you alot doc
You make understanding EKG really easy! This is what exactly I’ve been searching for! Thanks a lot!!!
awesome video tnx
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Omg you just made it seem so simple than what my biology book was blabbering on about.
what does it mean when the P wave is inverted?
the u wave is due to contraction of the papillary muscle .. small,positive, and rare wave
and the atria Re-polarization is masked by the stronger QRS complex ( ventricles depolarization ) because they happen at the same time 😉 ..hoped i helped
I was told that the U wave is due to electrolyte imbalance
some sort of action potential but for what????
That the direction of electrical depolarization is retrograde to what it normal is. When seen in lead 2, it implies the vector is moving away from Lead 2 (when you think of Einthoven’s triangle)
excuse me how come the t wave is repolarizing if the hump is going up isnt that depolarization?
Could you do a video on what an ekg look like when the leads are placed on backward.
the vector is going in the opposite direction than of depolarisation. thats why it is upward.
Source : Guyton.
NICE NICE NICE . Thanks a lot sir …
THANK YOU VERY GOOD INFORMATION !!!!
its safe to say your bloody fantastic!! i reckon ive passed all my previous subject because of you!
good explanation… tqvm
good
nice for learners
gud explanation
thanks for this video
can you tell me what is the difference between a QS wave and a necrosis Q wave
This might come as a stupid question but why doesnt the atria repolarize? Is this somhow masked by the QRS complex? Like if its inside/behind the QRS complex. Is this wrong? Or is there some other explanation?
that is correct
It is masked by the QRS complex
It is masked by the QRS complex
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