Harvard Heart Letter

A number worth watching

The heart's ejection fraction can be a helpful number to know.

A few ounces at a time, your heart moves about 2,000 gallons of blood a day. On the surface, the pumping process seems simple. The heart's upper chambers, the atria, relax and fill with blood. They squeeze, sending their contents to the ventricles below. Once full, the ventricles contract, pushing blood to all parts of the body.

There's more to it, of course, involving electrical pathways, valves, and a host of other elements. One of the intricacies is how much blood the heart sends into circulation with each beat. No matter how forceful, contractions don't squeeze out every last drop of blood from a chamber; some is left behind. The ratio of the amount of blood ejected, or pumped, with each beat to the amount the chamber holds when it is relaxed is called the ejection fraction. It can be a helpful guide for some people with heart disease.

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