What happens to the AV valves during isovolumetric contraction?

During isovolumetric contraction, the atrioventricular (AV) valves close as the ventricles begin to contract. This phase occurs after the ventricles have filled with blood but before they eject it into the aorta and pulmonary artery. The closure of the AV valves prevents the backflow of blood into the atria, and this action leads to the first heart sound, commonly referred to as S1, which signifies the start of ventricular contraction.

This phase is characterized by a rise in ventricular pressure while the ventricular volume remains constant because all valves (AV and semilunar) are closed. The closure of the AV valves is essential for the proper function of the heart, ensuring that the pressure generated by the ventricles effectively pushes blood into the arteries once the semilunar valves are opened. The distinct sound produced by this closure helps clinicians assess heart function and can be an important diagnostic tool.