Which statement best describes the relationship between ejection fraction and end-systolic volume?

• A. Ejection fraction is the proportion of end-diastolic volume ejected; end-systolic volume is the volume remaining after contraction.
• B. Ejection fraction equals end-diastolic volume; end-systolic volume equals stroke volume.
• C. Ejection fraction measures venous return; end-systolic volume measures heart rate.
• D. Ejection fraction and end-systolic volume are unrelated.

Answer: (A)

This question tests how the heart’s pumping efficiency is quantified. Ejection fraction describes the portion of the ventricle’s end-diastolic volume (the amount filled before contraction) that is ejected during systole, while end-systolic volume is the volume remaining in the ventricle after contraction. The relationship can be expressed as EF = SV/EDV, with SV = EDV − ESV, so EF = (EDV − ESV)/EDV. This means a larger end-systolic volume (less complete emptying) lowers the ejection fraction, whereas a smaller ESV (more complete emptying) raises it. The other statements misdefine these concepts—EF is not simply equal to EDV, end-systolic volume is not a measure of venous return or heart rate, and EF and ESV are indeed related through the heart’s contraction dynamics.