EasyZoologyBody fluid and circulation
+4 / -1
The 'lub' sound heard during the heartbeat is caused by:
A
Closing of semilunar valves
B
Closing of atrioventricular valves
C
Opening of semilunar valves
D
Opening of atrioventricular valves
Explanation
The 'lub' (first heart sound, S1) is caused by the closing of the atrioventricular valves (bicuspid and tricuspid valves) at the beginning of ventricular systole. The 'dub' (second heart sound, S2) is caused by the closing of semilunar valves at the end of ventricular systole.
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