Cardiac cycle.

Cardiac Cycle

Diastole

Atria and ventricles relax, expanding which draws blood into the atria.

Pressure in the atria increases opening the atrioventricular valves

blood passively enters the venticles

Semi-lunar valves are closed to prevent blood from leaving the heart.

Atrial Systole

Atria contract, forcing remaining blood into the ventricles.

Ventricular systole.

Ventricles contract, increasing pressure closing the atrioventricular valves to prevent back flow into the atria.

Semi-lunar valves are forced open as blood is ejected from the ventricles into the aorta and pulmonary artery.