Lessons · Medicine foundations · ejection fraction
Ejection fraction: the share of a full ventricle that leaves
Ejection fraction is the stroke volume divided by the volume in the ventricle at the end of filling, written as a percentage.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
It is the one number from an echocardiogram report that everybody quotes, and it is a fraction, not a volume. Knowing that the denominator is the full ventricle and not the empty one is the difference between a figure that makes sense and a figure above one hundred percent.
How to think about it
If you are given the two volumes, subtract to get the stroke volume first. Then divide by the end-diastolic volume, the fuller of the two. Multiply by 100 for a percentage. The answer is always between zero and one hundred; anything else means the division went the wrong way up.
Worked example
End-diastolic volume 120 mL, end-systolic volume 50 mLFull, then empty. The bigger number is the full one.
Stroke volume = 120 − 50 = 70 mLWhat actually left the ventricle in one beat.
EF = 70 / 120 = 0.583, a fraction of oneDivided by the full volume, never by the empty one.
0.583 × 100 = 58.3 %As a percentage, to one decimal place.
Your turn
The end-diastolic volume is 140 mL and the stroke volume is 63 mL. Write the line that gives the ejection fraction as a percentage.
EF = 63 / 140 × 100 = %
Solve one, graded on the server
The trap
Dividing by the end-systolic volume. It is the smaller number, so the answer comes out bigger than one hundred percent, which is the arithmetic telling you plainly that the denominator is wrong.