Ans. As the heart is a myogenic organ, the cardiac cycle is regulated intrinsically by nodal tissues. It is known to be intrinsic because it is initiated at the SA node present in the right atrium. SAN (sinoatrial node) initiates the processing of action potential, which is then conducted to AVN (atrioventricular node) and from AV bundle to bundle of His and then to ventricular musculature. In each cardiac cycle, there is systole and diastole of both atria and ventricles.