end-systolic volume
End-systolic volume is the blood left behind after the ventricle finishes squeezing — the low-water mark, the reserve the heart never empties. The chamber is at its smallest at this moment.
It is measured at the end of systole, just as the outlet valve closes. In a typical adult left ventricle it is around 50 milliliters. A more forceful or less obstructed contraction leaves less behind, lowering end-systolic volume.
End-systolic volume is sensitive to contractility and afterload: stronger muscle empties the chamber more completely, while a high afterload leaves more blood stuck inside. A rising end-systolic volume over time can be an early sign of weakening pump function.
It is the partner of end-diastolic volume in the stroke-volume equation — what the ventricle started with minus what it kept. A heart that empties poorly carries a large residual volume, which is reflected in a lower ejection fraction.
If a strong inotropic stimulus makes the left ventricle empty more completely, its end-systolic volume drops, raising stroke volume even without extra filling.
A more complete squeeze lowers residual (end-systolic) volume.
On a pressure–volume loop, end-systolic volume marks the leftmost point, where ejection ends. Tracking how it changes with load reveals the muscle's contractile state.