The second heart sound (dup) is the sound of the a. pacemaker initiating its contraction. b. blood..

The second heart sound (dup) is the
sound of the

a. pacemaker initiating its
contraction.

b. blood entering the aorta.

c. closing of the semilunar valves.

d. closing of the atrioventricular
(AV) valves.