When is the P wave seen on an ECG?

The P wave on an electrocardiogram (ECG) represents the electrical activity associated with the depolarization of the atria. This depolarization is the first step in the cardiac cycle, leading to atrial contraction and the subsequent filling of the ventricles with blood. The P wave precedes the QRS complex, which indicates ventricular depolarization.

Understanding the phases of cardiac electrical activity is crucial in distinguishing the significance of the P wave. During atrial depolarization, an electrical impulse spreads through the atrial muscle, activating them to contract and push blood into the ventricles. This process is essential for effective heart function and maintaining proper blood flow throughout the body.

The other choices pertain to different phases of the cardiac cycle. Atrial repolarization is not visible on the ECG since it typically occurs at the same time as the QRS complex, and therefore, is masked by it. Ventricular depolarization corresponds to the QRS complex, while ventricular repolarization is represented by the T wave. This differentiation highlights the importance of understanding when specific electrical events occur within the cardiac cycle, with the P wave clearly representing the atria's depolarization.