End-diastolic volume is defined as the amount of blood in each ventricle at the end of ventricular diastole.

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End-diastolic volume reflects how much blood the ventricles hold at the moment they are about to contract. During ventricular diastole the heart relaxes and fills from the atria, and the end of this filling phase is when the ventricles are at their maximum volume for that beat. That maximum filling volume is the end-diastolic volume, and it sets the starting point for the next beat’s pump: more EDV means more stretch of the ventricular muscle fibers, which can produce a stronger contraction and a larger stroke volume (within normal limits).

This concept is different from the amount pumped per minute (cardiac output), which is about how much blood is moved through the circulatory system each minute. It’s also not the amount in the arteries after systole—the arterial volume reflects blood ejected during the contraction and the arterial system’s properties. And it is not the amount in the ventricles after systole, which would be the end-systolic volume (the leftover blood after contraction).