During the cardiac cycle, the mitral valve closes at the START of which phase?

• A Rapid ventricular filling
• B Atrial systole
• C Rapid ejection
• D Isovolumetric contraction ✓

Explanation

The mitral valve closes at the onset of isovolumetric contraction — when rising LV pressure exceeds left atrial pressure at the end of diastole. This corresponds to the S1 heart sound. The mitral valve remains closed throughout systole (isovolumetric contraction, rapid ejection, reduced ejection) and opens again at the onset of rapid ventricular filling when LV pressure falls below left atrial pressure in early diastole.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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