The "lub" heart sound is due to the

A) onward rush of blood to the heart.
B) contraction of aortic muscle tissue.
C) closing of the semilunar valves.
D) closing of the atrioventricular valves.
E) the recoil of the aorta following the ventricle contraction.

Atrioventricular Valves

Heart valves located between the atria and ventricles, enabling blood flow from the atria to the ventricles while preventing backflow.

Semilunar Valves

Valves located at the exit of both the left and right ventricles of the heart, which prevent backflow of blood into the ventricles.

Ventricles

Ventricles are chambers within the heart that pump blood out to the lungs and the rest of the body, crucial for the cardiac circulation process.