During isovolumetric contraction, which valves are closed?

• A. Aortic valve and pulmonary valves are closed.
• B. All four valves open.
• C. Only the aortic valve is closed.
• D. Both the mitral and tricuspid valves are closed.

Answer: (D)

Isovolumetric contraction occurs when the ventricles contract and pressure rises but no blood moves in or out because all valves are momentarily closed. The mitral and tricuspid valves close first as ventricular pressure exceeds atrial pressure, preventing backflow into the atria. At the same time, the aortic and pulmonary valves are still closed because the ventricular pressure has not yet surpassed the pressures in the aorta and pulmonary artery. So, the phase is defined by a closed setup on both sides of the heart, keeping the ventricular volume constant. The option noting that the mitral and tricuspid valves are closed reflects this key feature, though the semilunar valves are closed as well during this moment.