Biologyhard · Past Paper
What causes the 'Lub' sound of the heart?
AClosing of semilunar valves
BOpening of AV valves
CClosing of AV valves
DOpening of semilunar valves
✓ Correct Answer: C — Closing of AV valves
The first heart sound (S1) or 'lub' is caused by the closure of the atrioventricular (mitral and tricuspid) valves.
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