Ejection fraction is one of the most widely quoted numbers in cardiology — the percentage of blood the left ventricle pumps out with each heartbeat. This guide explains how it's calculated from ventricular volumes, what the standard classification bands mean, and why EF alone doesn't tell the whole story about heart function.
What EF actually measures
Ejection fraction compares two ventricular volumes captured at different points in the cardiac cycle: end-diastolic volume (EDV), the ventricle's volume at its fullest just before it contracts, and end-systolic volume (ESV), what's left right after contraction. The difference, EDV − ESV, is the stroke volume — the absolute amount of blood ejected per beat. Ejection fraction simply expresses that stroke volume as a percentage of the ventricle's starting capacity: EF = (EDV − ESV) ÷ EDV × 100.
In practice, EDV and ESV are measured by echocardiography (most common), cardiac MRI, or nuclear imaging — not typically calculated by hand. This calculator performs the arithmetic step once you already have those two volumes from an imaging report.
The classification bands and why they matter
This calculator uses four general adult EF reference bands: normal reference range (≥55%), mildly reduced (41–49%), borderline / mildly reduced (50–54%), and reduced (≤40%). These bands are useful context but are not diagnoses. Heart failure with reduced ejection fraction (HFrEF) and heart failure with mildly reduced ejection fraction (HFmrEF) require symptoms and additional clinical evidence. Heart failure with preserved ejection fraction (HFpEF) also cannot be diagnosed from EF alone.
EF can vary with imaging modality, contouring method, loading conditions, and measurement quality. Compare serial values in the same clinical context and rely on the interpreting clinician's report.
What EF doesn't tell you
A single EF number is a snapshot of pumping function, not a complete diagnosis. It doesn't capture diastolic function (how well the ventricle relaxes and fills), valve disease, wall motion abnormalities in specific segments, or symptoms — all of which factor into a heart failure diagnosis alongside EF. EF also varies somewhat by measurement method and by the specific imaging study, so trends across serial echocardiograms (for example, before and after starting a new heart failure therapy) are often more clinically meaningful than one isolated reading.
This calculator is an educational and screening aid for working with EDV/ESV values you already have — it does not diagnose heart failure, interpret an echocardiogram, or substitute for a cardiologist's assessment.