Ejection fraction

What it means

Ejection fraction measures the percentage of blood the left ventricle — the heart's main pumping chamber — squeezes out with each heartbeat, relative to the total volume it held right before contracting. If the ventricle fills with 100 millilitres of blood and pushes out 60 of it, the ejection fraction is 60 percent. It is one of the single most-used numbers in cardiology because it captures, in one figure, how well the heart's pumping function is holding up.

Why it appears on a CT or MRI report

Cardiac MRI and cardiac CT can measure the volume of the left ventricle at its fullest (end-diastole) and its most contracted (end-systole) across the heartbeat cycle, and the ejection fraction is calculated directly from that difference. It's reported as a percentage, sometimes alongside the actual chamber volumes and the muscle wall's thickness and motion. Because these scans capture the heart in motion over many phases, they're considered a very precise way to measure this number, often used to double-check or refine a figure first estimated on echocardiogram.

What it usually means

A normal ejection fraction, generally 55 to 70 percent, means the left ventricle is emptying efficiently with each beat. A mildly reduced value (41–49 percent) can be an early or borderline finding. A clearly reduced ejection fraction — typically under 40 percent — points toward the heart muscle pumping less forcefully than it should, which can result from a prior heart attack, long-standing high blood pressure, valve disease, viral or other heart-muscle damage (cardiomyopathy), or a range of other causes your doctor will work through. It's also possible to have heart-failure symptoms with a normal or near-normal ejection fraction, since the number reflects pumping strength but not how well the heart relaxes and fills — a separate but related aspect of heart function.

When to follow up

A normal ejection fraction on a scan done for another reason is generally reassuring and needs no separate action. A reduced number, or one accompanied by symptoms such as shortness of breath, swelling in the legs, fatigue, or difficulty lying flat, warrants a prompt conversation with a cardiologist, who can look at the whole picture — including the likely cause — and discuss treatment, which is often very effective at improving both the number and how you feel.

A plain-language way to picture it

Think of the heart's main chamber as a hand squeezing a water balloon. A strong, complete squeeze pushes most of the water out each time — a high percentage. A weaker or less complete squeeze leaves more water behind in the balloon after each squeeze — a lower percentage. Ejection fraction is simply a measurement of how thorough that squeeze is, beat after beat.