Normal Heart Sounds are Caused by Which of the Following

Question

Normal heart sounds are caused by which of the following events?
A) friction of the blood against the chamber walls
B) opening and closing of heart valves
C) excitation of the SA node
D) closure of the heart valves

Accepted Answer

Normal heart sounds are primarily caused by the closure of the heart valves, specifically the atrioventricular valves (producing the "lub" sound) and the semilunar valves (producing the "dub" sound).