Between which two sounds does ventricular contraction occur?

Ventricular contraction, also known as systole, occurs between the first heart sound (S1) and the second heart sound (S2). S1, which is produced by the closure of the atrioventricular (AV) valves (the mitral and tricuspid valves), marks the beginning of ventricular contraction as the ventricles contract to pump blood into the aorta and pulmonary artery. This contraction continues until the closure of the semilunar valves (the aortic and pulmonic valves), which generates the second heart sound (S2). The closure of these valves signals the end of ventricular contraction and the beginning of diastole, where the heart chambers fill with blood again.

Understanding the timing of these heart sounds in the cardiac cycle is essential for recognizing normal and abnormal heart function, particularly in conditions like heart failure, where the mechanics of contraction and relaxation may be impaired.