What sound corresponds to the closing of the mitral and tricuspid valves?

The sound that corresponds to the closing of the mitral and tricuspid valves is known as the first heart sound, commonly referred to as S1. This sound occurs at the beginning of ventricular contraction (systole), when the ventricles are filled with blood and the pressure rises sufficiently to close the atrioventricular valves—the mitral valve on the left side of the heart and the tricuspid valve on the right side. The closure of these valves prevents the backflow of blood from the ventricles into the atria and is an important part of the cardiac cycle.

S1 is produced by the vibrations of the heart muscle and surrounding structures during the rapid closure of these valves, leading to a distinct sound that can be auscultated using a stethoscope. This first heart sound is typically louder and has a lower frequency than the second heart sound (S2), which is associated with the closure of the aortic and pulmonic valves at the end of ventricular systole.

In contrast, the second heart sound (S2) refers to the closing of the semilunar valves (aortic and pulmonic), while the third heart sound (S3) is associated with rapid ventricular filling during early diastole, and the