What does the S2 heart sound indicate?

The S2 heart sound is specifically associated with the closing of the semilunar valves, which include the aortic and pulmonary valves. This sound occurs at the end of ventricular systole when the ventricles have finished contracting and the blood has been ejected into the aorta and pulmonary artery. The closure of these valves prevents the backflow of blood into the ventricles as they begin to relax, contributing to the sound produced.

Understanding the timing of the S2 heart sound in relation to the cardiac cycle is crucial for interpreting heart sounds correctly and assessing cardiac function. While ventricular contraction is indicated by the earlier heart sound (S1), and atrial filling is a phase that occurs later in the cycle, it is the closure of the semilunar valves that defines the S2 sound. This distinction helps in recognizing normal heart sounds from abnormal findings during auscultation.