What is the lub-dub sound of a heartbeat?

Question

A.
atria contracting followed by the ventricles

B.
pacemaker controlling the heart rate

C.
blood moving through the arteries and veins

D.

Answer 1

The lub-dub sound of a heartbeat is best described by:

A. atria contracting followed by the ventricles.

To elaborate, the "lub" (first heart sound) occurs when the atrioventricular (AV) valves close as the ventricles contract, and the "dub" (second heart sound) occurs when the semilunar valves close after the ventricles eject blood into the arteries.