During which phase are the AV valves open and the SL valves closed?

During the phase of ventricular filling, the atrioventricular (AV) valves are open, allowing blood to flow from the atria into the ventricles. This phase occurs when the heart is in diastole, which is the relaxation phase of the cardiac cycle. During this time, the pressure in the ventricles is lower than in the atria, resulting in the opening of the AV valves.

Simultaneously, the semilunar (SL) valves are closed to prevent blood from flowing back into the ventricles from the aorta and pulmonary artery as the ventricles fill with blood. This is crucial for the proper function of the heart, as it ensures that the ventricles have enough volume to generate the pressure needed for the next phase of the cardiac cycle, which is ventricular ejection. The opening of the AV valves and the closure of the SL valves during this filling phase are vital for efficient heart function and maintaining proper circulation.