Which phase of the cardiac cycle involves ventricular ejection of blood into the aorta and pulmonary arteries?

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

Answer: (D)

The phase when blood is pumped out of the ventricles into the aorta and pulmonary arteries is ventricular ejection. In this stage, the ventricles contract powerfully, raising their pressure above the pressures in the aorta and pulmonary arteries. This pressure difference opens the semilunar valves, allowing blood to be ejected into the systemic and pulmonary circulations.

This contrasts with atrial systole, which is the atria contracting to finish filling the ventricles; isovolumetric contraction, where the ventricles contract but all valves are closed so the ventricular volume doesn’t change; and isovolumetric relaxation, when the ventricles relax with all valves closed.