Physiology question

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.


New Member
10+ Year Member
Feb 1, 2008
Reaction score

Members don't see this ad.

I've several questions conerning the ECG if someone has time to help out.

1) My teacher said that in the ventricles: last depolarization, first repolarization.
He mentioned that it was due to the plateu of action potential happening earlier. How is that?

2) How come T and P-waves can either be negative or positive? Shouldn't

If you know any good websites explaining ECG, it would be great to post them too.

I appreciate your input.


Full Member
10+ Year Member
Aug 30, 2007
Reaction score
Search for "EKG books" and other related topics on the SDN
wikipedia tells you something about everything. you can start from there.

I dont understand your first question

Im going to take a stab at the second question, which I also dont understand. Waves are negative or positive depending on what Lead you are looking at. The Leads are in different locations (Einthoven's Triangle). The waves in that lead are positive where the electical impulse is moving toward, or in the direction of the lead. They are negative where the impulse is moving away from, or against that lead.

T waves are almost always positive in all leads. The exceptions are Leads aVR, and sometimes V1. Negative T waves in the other leads make you think of bad things.