Question
Which one of the following is mainly responsible for the second heart sound?
Closure of atrioventricular valves
Opening of atrioventricular valves
Closure of semilunar valves
Thrust of blood on ventricular wall during atrial contraction
Solution
C.
Closure of semilunar valves
The first heart sound Lubb' is produced at the onset of ventricular systole, when the atria-ventricular valves (tricuspid and bicuspid) close. At the beginning of ventricular diastole, the semilunar valves close, producing the second heart sound 'dup'.
