What is responsible for closing the AV valves?

The closure of the AV (atrioventricular) valves is primarily due to increasing ventricular pressure. During ventricular systole, when the ventricles contract, the pressure within the ventricles rises significantly. This increase in pressure forces the AV valves—located between the atria and ventricles—to close, preventing the backflow of blood into the atria. As the ventricles contract and push blood into the arteries, the pressure builds up to a level that exceeds the pressure in the atria, effectively sealing the AV valves shut.

This mechanism is crucial for ensuring that blood flows in the correct direction—from the atria into the ventricles during diastole, and from the ventricles into the arteries during systole—maintaining efficient circulation throughout the heart and body. Understanding this process highlights the importance of ventricular pressure in the functioning of the heart and in cardiac physiology as a whole.