During isovolumetric contraction, which statements are true?

• A. Isovolumetric contraction occurs when the aortic valve opens.
• B. Isovolumetric contraction occurs when the mitral and tricuspid valves are closed and LV pressure rises without a change in volume.
• C. Isovolumetric contraction occurs during ventricular filling.
• D. Isovolumetric contraction occurs after the mitral valve opens.

Answer: (B)

Isovolumetric contraction is the brief phase of early systole when the ventricles contract but no blood leaves them because all valves are closed. This happens after the mitral and tricuspid valves have shut and before the aortic and pulmonary valves open. The ventricle’s pressure rises as the muscle contracts, yet the volume remains constant since there’s no ejection through the semilunar valves yet. The aortic valve only opens once the LV pressure exceeds the aortic pressure, which starts the ejection phase. Ventricular filling occurs earlier, during diastole, when the mitral valve is open; that’s not part of isovolumetric contraction.