What does the P wave represent in an electrocardiogram?

The P wave in an electrocardiogram (ECG) is significant because it represents the depolarization of the atria, which is the electrical activity that leads to the contraction of the atrial muscles. This contraction follows the depolarization and results in the pumping of blood from the atria into the ventricles. Understanding the P wave is crucial as it reflects the normal sequence of electrical events in the heart, starting with the sinoatrial (SA) node firing and spreading through the atria, ultimately facilitating an efficient cardiac cycle.

The other options do not correctly define the P wave. The indication of ventricular contraction is represented by the QRS complex, not the P wave. The resting phase of the heart cycle, known as diastole, occurs after the heart has contracted, which is not reflected in the P wave. Lastly, heart rate variability is a broader measurement that assesses variations in heart rate over time and does not correspond to the specific representation of the P wave itself.