P wave indicates

The correct option is Depolarization of both atria.

An electrocardiogram (ECG or EKG) is a medical test that records the electrical activity of the heart over a period of time. A normal ECG cycle consists of several distinct electrical waves, namely the P wave, the QRS complex, and the T wave. Each of these waves corresponds to a specific electrical event in the heart's cardiac cycle.

The P wave is the first wave visible in a normal ECG. It represents the electrical impulse spreading through the upper chambers of the heart, which are the right and left atria. This electrical activation process is known as depolarization. Under normal physiological conditions, the electrical impulse originates in the sinoatrial (SA) node (the heart's natural pacemaker) located in the right atrium. The impulse then spreads rapidly across both the right and left atria, causing them to depolarize almost simultaneously. This atrial depolarization triggers the mechanical contraction of the atrial muscle, pumping blood into the ventricles. Therefore, the P wave directly indicates the depolarization of both atria.