Closure of the semilunar valves and opening of the atrioventricular valves is associated with which heart sound?

a. S1 c. S3
b. S2 d. S4

ANS: B
The second heart sound occurs at the beginning of ventricular relaxation and is associated with closure of the semilunar valves and opening of the atrioventricular valves. The first heart sound occurs at the onset of ventricular contraction and is associated with closure of the atrioventricular valves and opening of the semilunar valves. The third heart sound occurs during early ventricular filling, and the fourth heart sound occurs during atrial contraction.