The second heart sound, dup, is produced by the closure of the
- A. atrioventricular valves
- B. semilunar valves
- C. coronary valves
- D. pulmonary veins
Explanation
When the ventricles relax, blood trying to flow back snaps the aortic and pulmonary semilunar valves shut, producing the shorter, sharper second sound. The first sound, lubb, comes from the atrioventricular valves closing.