What does the P wave on an ECG represent?

The P wave on an ECG represents atrial depolarization. This is the electrical activity that occurs in the heart when the atria contract to push blood into the ventricles. During this process, the atrial muscle cells are activated, leading to a wave of electric charge that spreads through the atria. The P wave precedes atrial contraction, making it an essential part of the cardiac cycle and an important indicator of atrial function on the ECG tracing.

Understanding the role of the P wave is critical for interpreting ECGs, as it provides insights into the atrial electrical activity and can help identify potential issues such as atrial enlargement or rhythm disturbances. The other choices relate to different phases of heart electrical activity; atrial contraction follows depolarization, while ventricular depolarization and repolarization pertain to the electrical events associated with the ventricles, which are represented by different parts of the ECG tracing.