What happens during isovolumic relaxation?

What happens during isovolumic relaxation?

• A. Ventricles are in diastole, and there is no change in ventricular blood volume.
• B. Ventricles contract and eject blood.
• C. Atria fill with blood, AV valves open.
• D. SL valves close.

Answer: (A)

Isovolumic relaxation is the brief early-diastole phase right after the ventricles finish contracting and the semilunar valves have closed. During this time, both the atrioventricular valves and the semilunar valves are closed, so the ventricles relax without either ejecting blood or filling. The ventricular volume stays constant (end-systolic volume), while the pressure inside the ventricles falls. When ventricular pressure drops below atrial pressure, the AV valves open and filling begins. This is why the key description is that the ventricles are in diastole with no change in ventricular blood volume.

Isovolumic relaxation is the brief early-diastole phase right after the ventricles finish contracting and the semilunar valves have closed. During this time, both the atrioventricular valves and the semilunar valves are closed, so the ventricles relax without either ejecting blood or filling. The ventricular volume stays constant (end-systolic volume), while the pressure inside the ventricles falls. When ventricular pressure drops below atrial pressure, the AV valves open and filling begins. This is why the key description is that the ventricles are in diastole with no change in ventricular blood volume.