During ventricular systole, what occurs?

• A. The atria contract
• B. The ventricles relax
• C. The ventricles contract and force blood from the ventricles into the arteries
• D. Blood enters the heart from the veins

Answer: (C)

Ventricular systole is the phase when the ventricles contract, raising the pressure inside them and pushing blood out into the arteries. This active ejection occurs when the semilunar valves open, sending blood into the aorta and pulmonary artery.

Atria contracting happens during atrial systole, which helps fill the ventricles before this phase. Ventricles relaxing occurs during ventricular diastole, when the heart chambers refill. Blood entering the heart from the veins happens during venous return, mainly during diastole and atrial systole, not during ventricular systole.