The first heart sound,"lub," is made by
A)closure of the AV valves.
B)closure of the semilunar valves.
C)contraction of the ventricles.
D)contraction of the atria.

Question

Quizplus · Accepted Answer

The first heart sound, "lub," is caused by the closure of the AV (atrioventricular) valves, which separate the atria and ventricles. This occurs at the beginning of systole, when the ventricles begin to contract and the pressure in the ventricles rises, causing the AV valves to snap shut.

The First Heart Sound,"lub," Is Made by