Isovolumetric contraction occurs when which valves are closed?

• A. Mitral and aortic valves closed
• B. Mitral and aortic valves open
• C. Only mitral valve closed
• D. Only aortic valve closed

Answer: (B)

Isovolumetric contraction is the part of ventricular systole when the ventricle is contracting but the volume stays the same. This happens because both valves controlling inflow and outflow are closed: the mitral valve has closed as the ventricular pressure rises above atrial pressure, and the aortic valve remains closed until the ventricle pressure is high enough to open it. With both valves shut, no blood enters or leaves the ventricle, so the pressure increases without a change in volume. When the ventricular pressure finally exceeds the aortic pressure, the aortic valve opens and ejection begins, ending the isovolumetric phase.