ANATOMY

Detailed explanation-1: -During systole, the two ventricles develop pressure and eject blood into the pulmonary artery and aorta. At this time the atrioventricular valves are closed and the semilunar valves are open. The semilunar valves are closed and the atrioventriular valves are open during diastole.

Detailed explanation-2: -The ventricles contract due to the ventricular depolarization and the pressure inside the ventricles rapidly increases. Immediately after a ventricular contraction begins, the pressure in the ventricles exceeds the pressure in the atria and thus the atrioventricular valves shut.

Detailed explanation-3: -The atrioventricular (AV) valve will close during ventricular systole. When the ventricles contract, the pressure within the ventricles will be higher than the pressure in the atria.

Detailed explanation-4: -As pressure drops within the ventricles, blood flows from the major veins into the relaxed atria and from there into the ventricles. Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves remain closed (see image below).

Detailed explanation-5: -This tension on the AV valve leaflets prevents them from bulging back into the atria and becoming incompetent (i.e., “leaky”). Closure of the AV valves results in the first heart sound (S1). This sound is normally split ( 0.04 sec) because mitral valve closure precedes tricuspid closure.