What event occurs at the start of diastole?

At the start of diastole, the heart ventricles begin to fill with blood following the relaxation of the myocardium. This event is marked by the closure of the aortic valve, which happens at the end of systole. The closure of the aortic valve prevents the backflow of blood into the left ventricle as the heart transitions to diastole.

As the aortic valve closes, the pressure in the aorta drops, and the heart muscle relaxes. This creates a negative pressure in the ventricles, allowing blood to flow from the atria into the ventricles. This sequence is crucial for the filling phase of the heart cycle, making it essential to understand that the closure of the aortic valve signifies the start of diastole.

Other events occurring, such as the closure of the tricuspid valve or the opening of the pulmonic valve, happen during different phases of the cardiac cycle. The production of the first heart sound (S1) is associated with the closure of the AV valves (mitral and tricuspid) and occurs at the beginning of systole, not diastole. Thus, closure of the aortic valve is the key event that marks the transition into the diast