Emergency Medical Technician (EMT) Intermediate Practice Exam

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What does the second heart sound (S2) represent?

Closure of the atrioventricular valves
Opening of the semilunar valves
Closure of the semilunar valves
Opening of the atrioventricular valves

The correct answer is: Closure of the semilunar valves

The second heart sound, referred to as S2, occurs primarily due to the closure of the semilunar valves, which include the aortic and pulmonary valves. This sound follows the ventricular contraction (systole) when the blood is pumped from the heart into the aorta and pulmonary artery. Once the ventricles finish contracting and begin to relax (diastole), pressure in the ventricles falls below that in the aorta and pulmonary artery, leading to the closure of the semilunar valves. This closure is a significant event in the cardiac cycle, marking the end of systole and the beginning of diastole. In contrast, the first heart sound (S1) is associated with the closure of the atrioventricular valves (the tricuspid and mitral valves), which occurs at the beginning of ventricular contraction. The opening of either semilunar or atrioventricular valves does not correspond to a heart sound but instead is related to the flow of blood into or out of the chambers. Therefore, S2 distinctly indicates the closure of the semilunar valves, signifying an important transition in the cardiac cycle.