The P wave represents the depolarization of the left and right atrium and also corresponds to atrial contraction. Strictly speaking, the atria contract a split second after the P wave begins. Because it is so small, atrial repolarization is usually not visible on ECG.

What does the P wave stimulate?

The first wave on an ECG is the P wave, indicating atrial depolarization in which the atria contract (atrial systole ).

What electrical events occur in the P wave?

The P wave results from atrial depolarization. The QRS complex is a result of ventricular depolarization and indicates the start of ventricular contraction. The T wave results from ventricular repolarization and signals the beginning of ventricular relaxation.