During which period are the ventricles relaxed and filling with blood?

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

Answer: (A)

Ventricular diastole is the phase when the ventricles are relaxed and filling with blood. As the ventricles relax, their pressure falls and the mitral and tricuspid valves open, allowing blood to flow from the atria into the ventricles. A large portion of filling happens passively, and toward the end of this period the atria contract to push in a final amount of blood (atrial kick). In contrast, ventricular systole is the contraction phase when the ventricles eject blood; atrial diastole is when the atria relax and fill, and atrial systole is when the atria contract. The description given corresponds to ventricular diastole.