ABSTRACT
The human heart contains four valves that ensure unidirectional blood fl ow throughout the cardiac cycle. The semilunar valves (pulmonary on the right side and aortic on the left) prevent retrograde fl ow back into the ventricles during diastole. The atrio-ventricular valves (tricuspid on the right and mitral on the left) prevent retrograde fl ow from the ventricle to the atrium when the heart contracts during systole. All four valves function passively, opening and closing due to inertial forces exerted by the fl owing blood. Although their function is seemingly simple, the biomechanical demands placed on the cardiac valves are substantial, and specialized valve tissue and cells have evolved to ensure proper function under conditions of extreme multi-modal loading repeated with every heartbeat.
