During which phase are both AV and SL valves closed?

The phase during which both the atrioventricular (AV) valves and the semilunar (SL) valves are closed is isovolumic ventricular contraction. In this phase, the ventricles are contracting, but the volume of blood within them remains constant because the valves are closed, preventing blood from entering or leaving the ventricles.

This occurs immediately after the ventricles have filled with blood during diastole and just before they begin to eject blood during ventricular ejection. The AV valves are closed to prevent backflow into the atria, and the SL valves remain closed until the pressure in the ventricles exceeds the pressure in the arteries, allowing for ejection.

Understanding this phase is crucial for grasping how the cardiac cycle functions, specifically the relationship between pressure changes and valve states during the contraction of the heart.