What does the P wave represent on an ECG?

The P wave on an ECG represents atrial depolarization, which occurs just before the atria contract and initiate atrial systole. During this phase, electrical impulses spread through the atria, leading to their contraction and the subsequent filling of the ventricles with blood. This is a crucial part of the cardiac cycle as it contributes to the overall efficiency of heart function by ensuring that the ventricles are adequately filled with blood before they themselves contract. Understanding this aspect is essential in distinguishing the various components of an ECG tracing and their physiological significance.