Medical Definition of ejection fraction
: the ratio of the volume of blood the heart empties during systole to the volume of blood in the heart at the end of diastole expressed as a percentage usually between 50 and 80 percent <An echocardiogram obtained 6 days after the initiation of chemotherapy showed that the ejection fraction had improved to 45%; 2 weeks later it was 66%.—Patrick T. O'Gara et al., The New England Journal of Medicine, 17 Dec. 2009>
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