Question

The second heart sound (S2) occurs when:

A. Systole begins
B. There is rapid ventricular filling
C. The mitral and tricuspid valves close
D. The aortic and pulmonic valves close

Answer 1

The second heart sound (S2), also known as "dub," occurs when the aortic and pulmonic valves close during the onset of ventricular diastole.

Step-by-step explanation:

The second heart sound (S2), commonly described as a "dub," occurs when the aortic and pulmonic valves close at the end of the ventricular systole as the ventricles begin to relax, which is known as ventricular diastole. The closure of these semilunar valves prevents the backflow of blood into the ventricles and generates the S2 sound. This event marks the end of the cardiac cycle known as systole and the beginning of diastole, where the heart is refilled with blood.