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

Clinical guidelines (following American Society of Echocardiography and ACC/AHA conventions) split adult left ventricular EF into three bands: normal (≥55%), mildly reduced (41–54%), and reduced (≤40%). These bands matter because they map onto distinct heart failure categories with different underlying mechanisms and different evidence-based treatments. Heart failure with reduced ejection fraction (HFrEF, EF ≤40%) responds to a well-established medication regimen — ACE inhibitors or ARNI, beta-blockers, mineralocorticoid receptor antagonists, and SGLT2 inhibitors — that has been shown in large trials to reduce mortality.

Heart failure with preserved ejection fraction (HFpEF, EF ≥50% with heart failure symptoms) is a different problem: the ventricle pumps a normal fraction of its volume, but often can't relax and fill properly between beats. The mildly-reduced band (HFmrEF) sits between the two and can share features of either, which is why it's treated as its own intermediate category in current guidelines rather than lumped with one side or the other.

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.