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 while relaxation is known as diastole

Both the atria and ventricles are relaxed Blood returning to the atria flows into the ventricles The higher pressure in the arteries close the semi lunar (SL) valves

Both atria contract and ventricles relax The remainder of the blood in the atrium is transferred through the open AV valves to the ventricles The SL valves are closed

The ventricles contract and the atria relax This closes the AV valves and pumps the blood out through the open SL valves to the aorta and the pulmonary artery

The opening and closing of the AV and SL valves are responsible for the heart sounds heard with a stethoscope