What does S2 heart sound represent?

The S2 heart sound is produced primarily by the closure of the semilunar valves, which include the aortic and pulmonary valves, at the end of ventricular systole. This occurs when the ventricles finish contracting and begin to relax, leading to a drop in ventricular pressure. As the pressure falls, the blood in the aorta and pulmonary artery pushes against the cusps of the semilunar valves, causing them to close, which is associated with the "dub" sound of the heartbeat.

This sound is significant as it marks the transition from systole to diastole and helps indicate that the heart is entering a phase where it will refill with blood. It is an important aspect of the cardiac cycle that healthcare providers listen for when assessing heart function.

The other options relate to different phases of the heart cycle. The closure of atrioventricular valves corresponds to the S1 heart sound, while contraction and relaxation of the heart muscles pertain to the mechanical actions of the cardiac cycle but do not directly represent specific heart sounds.