What is represented by the P wave in an ECG?

The P wave in an ECG represents the depolarization of both the right and left atria. This phase of the cardiac cycle is crucial as it precedes atrial contraction, also known as atrial systole. During depolarization, the electrical impulse spreads through the atria, causing them to contract and push blood into the ventricles.

The significance of the P wave reflects the initial electrical activity in the heart that sets the stage for effective blood circulation. Understanding this helps in interpreting the overall heart rhythm and can indicate conditions related to atrial function. The other options relate to different phases of heart activity and do not correctly describe what the P wave signifies.