ejection fraction
Ejection fraction is the percentage of a full ventricle's blood that gets pushed out with each beat — how much of the tank empties per stroke. It is one of the most quoted single numbers in cardiology.
It equals stroke volume divided by end-diastolic volume, written as a percentage. A normal left ventricle ejects roughly 55 to 70 percent of its contents each beat; it never fully empties, so even a healthy ejection fraction is well below 100 percent.
A reduced ejection fraction signals a weakened squeeze and defines one major form of heart failure. But a normal ejection fraction does not guarantee a healthy heart: some patients have heart failure with a preserved ejection fraction, where the problem lies in stiff, poorly relaxing ventricles rather than weak contraction.
Because it is a fraction, ejection fraction can stay normal even when total output is low (if the ventricle is small) or look low when the ventricle is large but still moving a fair amount of blood. It is informative but should be read alongside symptoms and other measures, not in isolation.
A stroke volume of 70 mL from an end-diastolic volume of 120 mL gives an ejection fraction of about 58 percent — within the normal range.
Divide what is ejected by what was held to get ejection fraction.
Ejection fraction = stroke volume ÷ end-diastolic volume × 100%. It is most often measured by echocardiography and is the basis for distinguishing HFrEF (reduced EF) from HFpEF (preserved EF).