During the P wave of an ECG, the atrial depolarization occurs. This is the initial phase where the electrical impulse that triggers the heartbeat starts in the sinoatrial (SA) node, which is the natural pacemaker of the heart. The impulse then travels through the atria, causing them to contract and pushing blood into the ventricles. The P wave on the ECG represents this atrial contraction. It is typically the first wave you see on an ECG and is followed by the QRS complex, which represents ventricular depolarization, and then the T wave, which represents ventricular repolarization. The wave of atrial repolarization, also known as the Ta wave, is often not visible on a standard 12-lead ECG due to its small amplitude and the fact that it is typically overlapped by the much larger QRS complex. read more >>

Atrial and ventricular depolarization and repolarization are represented on the ECG as a series of waves: the P wave followed by the QRS complex and the T wave. The first deflection is the P wave associated with right and left atrial depolarization. Wave of atrial repolarization is invisible because of low amplitude.read more >>