The first heart sound
A)occurs when the AV valves open
B)occurs when the semilunar valves close
C)signals the onset of ventricular diastole
D)occurs when the AV valves close, and signals the onset of ventricular systole
E)occurs when the semilunar valves close, and signals the onset of ventricular diastole

Question

Quizplus · Accepted Answer

The first heart sound, commonly referred to as "lub," occurs when the AV valves (tricuspid and mitral) close at the beginning of ventricular systole. This sound signals the onset of ventricular contraction and the closure of the valves prevents blood from flowing back into the atria.

The First Heart Sound