The cardiac cycle refers to the pattern of contraction and relaxation of the heart during one complete heartbeat.
Contraction of the heart muscle is known as systole and relaxation of the heart muscle is called diastole.
The cardiac cycle has 3 stages:
Functions of the heart
The 'lubb dubb' heart sounds heard through a stethoscope are the sounds of the atrioventricular (AV) valves and semilunar (SL) valves opening and closing.