The cardiac cycle consists of two main phases: systole and diastole. During systole, the ventricles contract, pumping blood out of the heart. During diastole, the ventricles relax and fill with blood from the atria. The cycle is regulated by the heart's electrical conduction system, including the sinoatrial (SA) node, atrioventricular (AV) node, Bundle of His, and Purkinje fibers, which coordinate the timing of contractions.
