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.

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