Doctors usually measure heart function percentage, or ejection fraction, using an echocardiogram test, according to the American Heart Association. MUGA and CAT scans, cardiac catheterization, and nuclear stress tests are also sometimes used. These tests determine how efficiently the heart pumps blood.
An ejection fraction test determines how much blood the heart’s left ventricle pumps with each contraction, reports the American Heart Association. Doctors commonly use this test to diagnose and track heart failure. Doctors interpret test results as percentages; for example, an ejection fracture of 65 percent means that the heart pushes out 65 percent of the total blood in the left ventricle with every beat.
The normal ejection fraction is 55 to 70 percent, notes the American Heart Association. Ejection fractions below 40 often indicate the presence of heart failure or cardiomyopathy, which is a condition characterized by enlargement of the heart muscle. Ejection fractions from 40 to 55 indicate damage to the heart, potentially from previous myocardial infarction. Ejection fraction readings of 75 or greater can indicate various heart conditions, including hypertrophic cardiomyopathy.
A normal reading on an ejection fraction test does not necessarily mean that heart failure is not present, reports the American Heart Association. Heart failure with preserved ejection fraction, or HFpEF, causes the heart to pump out less blood than normal.