The cyclic events that occur in each heartbeat together are called a cardiac cycle. which completes in about 0.8 seconds and includes the following events.

The right auricle receives deoxygenates blood from the body through openings of the vena cavae. while the left auricle received oxygenated blood from the lungs, through four pulmonary veins. The flow of blood in the right auricle stimulates the SA node which generates the impulse of the first contraction. This impulse is spread out over the walls of both auricles as a wave of contraction.

As a result, the auricles contract simultaneously and push the blood into the respective ventricles through AV apertures. The auricular systole lasts for 0.1 seconds.

During ventricular systole deoxygenated blood from the right ventricle is pumped into the lungs for oxygenation while oxygenated blood from the left ventricle is pumped into the systemic aorta which districts the blood to all parts of the body. Contraction of the left ventricle is stronger than the contraction of the right ventricle. Ventricular contraction is brought about by the AV node, a Bundle of His and Purkinje fibres. ventricular systole lasts for 0.3 seconds.

During joint diastole both the auricles and ventricles undergo relaxation hence also called complete cardiac. During diastole backflow of the blood from the aorta into the ventricles is prevented by the closing of semilunar Valves. During this phase, auricles get filled with respective blood and the new cardiac cycle begins. The joint diastole lasts for about 0.4 seconds.

Thus one cardiac cycle is completed in about 0.8 seconds.