ECG waveforms including the P wave, QRS spike, and T wave provide electronic signatures of atrial and ventricular contractions and repolarization.

“in a, every time the heart beats, there's a signature that can be measured electronically when you put leads on the chest and you have a a little wave that symbolizes when the atrium is doing its contraction. That's called the P wave. Then you have the big signal, which is this QRS spike, and that's this ventricular contraction. And then you have another little wave called a T wave. And I can't even remember, is that the repolarization? Yeah. Ventricular repolarization. Ventricular repolarization.”