Depolarization and repolarization are critical processes in the electrical activity of the heart that allow it to contract and pump blood effectively. Here's a detailed explanation: Depolarization is the process by which the heart muscle cells, known as cardiomyocytes, undergo a change in their electrical charge from a resting state to an active state. This change is initiated by the sinoatrial (SA) node, which is the heart's natural pacemaker. The SA node sends out an electrical impulse that travels through the atria, causing them to contract and push blood into the ventricles. This atrial contraction is represented by the P wave on an electrocardiogram (ECG). The impulse then reaches the atrioventricular (AV) node, which delays the signal by about 100 milliseconds to allow the atria to finish contracting. After this delay, the impulse is transmitted to the ventricles, causing them to contract and pump blood out of the heart. The ventricular contraction is represented by the QRS complex on an ECG. Repolarization occurs after depolarization and is the process by which the heart muscle cells return to their resting state. This is a critical phase that prepares the cells for the next depolarization. During repolarization, the electrical charge of the cells goes from a positive to a negative state, and this is represented by the T wave on an ECG. Both depolarization and repolarization are essential for the proper functioning of the heart. Any disruption in these processes can lead to cardiac arrhythmias, which are abnormal heart rhythms that can be life-threatening. read more >>

Depolarization occurs in the four chambers of the heart: both atria first, and then both ventricles. ... The SA node sends the depolarization wave to the atrioventricular (AV) node which��with about a 100 ms delay to let the atria finish contracting��then causes contraction in both ventricles, seen in the QRS wave.read more >>