What causes the first heart sound during the cardiac cycle?

Show Answers

Shutting of the aortic and pulmonary semilunar valvesThe aortic and pulmonary valves openingClosing of the mitral and tricuspid atrioventricular valvesOpening of the mitral and tricuspid valves

Explanation

The first heart sound (S1) is generated by the closure of the mitral and tricuspid valves at the beginning of ventricular contraction. This prevents backflow of blood into the atria. The closing of the aortic and pulmonary valves produces the second heart sound (S2).