Concerning heart sounds, which of the following is correct?

A) The first heart sound occurs at the beginning of ventricular systole.
B) The second heart sound is heard when the AV valves are closing.
C) The first heart sound is the sound of the semilunar valves closing.
D) The second heart sound occurs when blood flows into the superior vena cava.
E) The first heart sound occurs at the beginning of ventricular diastole.

Ventricular Systole

Ventricular systole is the phase of the cardiac cycle during which the ventricles contract, pumping blood out of the heart and into the circulatory system.

Semilunar Valves

Heart valves located between the ventricles and the major arteries leaving the heart, which prevent the backflow of blood.

AV Valves

Atrioventricular (AV) valves are valves located between the atria and ventricles of the heart that prevent backflow of blood from the ventricles into the atria during contraction.