What event is associated with the S1 heart sound?

The S1 heart sound is primarily associated with the closing of the atrioventricular (AV) valves, which includes the mitral and tricuspid valves. This sound marks the beginning of ventricular systole, where the ventricles contract to pump blood out of the heart. When the ventricles fill with blood during diastole, the AV valves are open; as the ventricles contract, these valves close to prevent the backflow of blood into the atria, leading to the distinct "lub" sound known as S1.

Understanding the S1 sound is crucial in cardiovascular assessments, as it reflects the functionality of the heart’s valves and the overall hemodynamic status of the patient. This sound is typically heard with a stethoscope placed over the chest, particularly at the apex of the heart, where the closing of the AV valves is best appreciated.