What Causes S₁ and S₂

Question

What causes S₁ and S₂?
A) Closure of heart valves
B) Firing of the SA node
C) Opening of heart valves.
D) Movement of the cardiac impulse along the His-Purkinje fibers

Accepted Answer

S₁ and S₂ are caused by the closure of the heart valves. S₁ is caused by the closure of the mitral and tricuspid valves at the start of systole, while S₂ is caused by the closure of the aortic and pulmonic valves at the end of systole.