Which option best describes diastole?

• A. The period when the ventricle is refilling
• B. The period of ventricular ejection
• C. The moment of atrial contraction
• D. The start of atrioventricular valve closure

Answer: (A)

Diastole is the relaxation phase of the heart cycle when the ventricles are filling with blood. As the heart muscle relaxes after contraction, the atrioventricular valves are open, allowing blood to flow from the atria into the ventricles, while the semilunar valves stay closed to prevent backflow. This filling continues until the ventricles are ready for the next contraction, with atrial contraction toward the end of diastole helping top off the ventricular filling.

This is why describing diastole as the ventricle refilling is the best answer. It’s not the period of ventricular ejection—that happens during systole when the ventricles contract and push blood out. While atrial contraction occurs during the latter part of diastole and contributes to filling, diastole itself refers to the overall relaxation and filling phase, not just that single moment. The start of AV valve closure marks the end of systole and the transition into diastole, so it does not define the entire diastolic phase.