End-diastolic volume refers to the volume of blood in the ventricle at what moment?

• A. End of systole
• B. During mid-diastole
• C. End of diastole, just before contraction
• D. Immediately after atrial contraction

Answer: (C)

End-diastolic volume is the amount of blood in the ventricle at the end of filling, right before the ventricle begins to contract. After the heart relaxes in diastole, the ventricles fill through rapid filling, a period of slower filling, and a final contribution from atrial contraction. When diastole ends, the ventricles hold their maximum volume for the cycle—this is the end-diastolic volume, the preload that sets how much blood they pump out with the next heartbeat. After this moment, the ventricles start contracting (isovolumetric contraction) and eject blood, so the volume drops to the end-systolic volume. It isn’t the end of systole (that’s after ejection), nor mid-diastole (filling is still progressing), nor the moment immediately after atrial contraction (the end of diastole is reached after atrial systole finishes and filling is complete).