The ventricles contract in which phase to eject blood into the pulmonary system or distal circulation?

• A. Ventricle diastole
• B. Atrial systole
• C. Ventricle systole
• D. Atrial diastole

Answer: (C)

During the cardiac cycle, the ventricles contract in the phase known as ventricular systole. This contraction generates enough pressure to open the semilunar valves, pushing blood from the right ventricle into the pulmonary circulation via the pulmonary valve and from the left ventricle into the systemic circulation via the aortic valve. Diastole is the relaxation phase when the ventricles fill with blood, and atrial systole is when the atria actively contract to aid ventricular filling. Atrial diastole is simply atrial relaxation. So, to eject blood into the pulmonary system or distal circulation, the ventricles must be in systole.