What does the S2 heart sound represent?

The S2 heart sound signifies the closure of the pulmonic and aortic valves at the end of ventricular systole, which occurs just before the ventricles begin to relax. When the ventricles contract and eject blood into the aorta and pulmonary artery, the pressure increases, causing the aortic and pulmonic valves to open. Once the ventricular contraction is completed and the pressure begins to drop, these valves close, resulting in the second heart sound, S2.

This sound is crucial as it marks the transition from ventricular contraction to relaxation, indicating that blood flow has moved from the ventricles into the systemic and pulmonary circulation and that the heart is preparing for the filling phase in diastole. The distinct sound of S2 is an important part of cardiac auscultation and helps healthcare providers assess heart function and identify potential issues.