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Figure 1 The mathematics of the ejection fraction. The normal pressure-volume loop is represented as a box that is confined by a line of contractility and a line of diastolic compliance. The ejection fraction (EF) is simply the width of the box (stroke volume [SV]) divided by the left ventricular end-diastolic volume (LVEDV). EDV = end-diastolic volume; ESV = end-systolic volume. AC = aortic closure; AO = aortic opening; MC = mitral closure; MO = mitral opening.