During the cardiac cycle, which phase is characterized by a rapid rise in left ventricular pressure with no change in volume as the mitral and aortic valves are closed?

• A. Isovolumetric contraction
• B. Isovolumetric relaxation
• C. Ventricular ejection
• D. Atrial contraction

Answer: (A)

During the early part of ventricular systole, both the mitral valve and the aortic valve are closed. The ventricle contracts and pressure inside rises rapidly, but the chamber volume stays the same because no blood can enter or leave. This is the phase where the heart builds pressure without a change in volume—isovolumetric contraction. It continues until left ventricular pressure exceeds aortic pressure and the aortic valve opens, allowing ejection to begin. The other phases involve valves moving (isovolumetric relaxation with valves closed but pressure falling; ventricular ejection with blood leaving; atrial contraction increasing filling) and do not match the description of a rapid pressure rise with no volume change.