During atrial systole, what occurs?

• A. The atria contract together.
• B. The ventricles contract.
• C. Blood is pumped from the ventricles into the arteries.
• D. Atrial contraction forces a small amount of additional blood into the ventricles.

Answer: (D)

During atrial systole the heart’s atria contract to finish filling the ventricles. This action, known as the atrial kick, pushes a small additional volume of blood into the ventricles, increasing their preload just before they begin to contract. That small boost in ventricular filling is the key consequence of atrial systole.

In other words, the atria do contract, but the most specific effect of this phase is delivering that extra amount of blood into the ventricles. Ventricular contraction and ejection occur later, during ventricular systole, so statements about the ventricles pumping blood into arteries describe a different phase of the cycle. Similarly, saying the atria contract together is true but less informative about what atrial systole accomplishes.