What action causes audible heart sounds?

Heart sounds are produced by the movement of blood through the heart and the closing of the heart valves. The first heart sound, S1, is caused by the closure of the mitral and tricuspid valves at the beginning of systole. The second heart sound, S2, is caused by the closure of the aortic and pulmonic valves at the end of systole.

The specific actions that cause these sounds are as follows:

- S1: When the ventricles contract, the pressure inside them increases. This causes the mitral and tricuspid valves to close, which produces a clicking sound.

- S2: When the ventricles relax, the pressure inside them decreases. This causes the aortic and pulmonic valves to close, which produces a more muffled sound.

The duration and intensity of heart sounds can vary depending on a number of factors, including age, sex, heart rate, and blood pressure.