How to Understand Left Ventricular Ejection Fraction and Cardiac Function Left ventricular systolic function has been used to evaluate the severity of cardiac disease and is a predictor of the occurrence of cardiovascular events and death. Although there are many metrics to evaluate LV systolic function, LV ejection fraction is the most commonly used metric to evaluate LV systolic function in clinical practice, and many laboratory’s routinely measure LV ejection fraction. Many units rely on linear methods of M-mode or 2D images to quantify LV systolic function, but the currently recommended method is the biplane disc method (a simplified Simpson method) to calculate LV volume and ejection fraction. The formula for calculating left ventricular ejection fraction (EF) is as follows: here, LVEDV = left ventricular end-diastolic volume; LVESV = left ventricular end-systolic volume. The recommended reference values for grading left ventricular function according to left ventricular ejection fraction are shown in the table. From the above formulae, it can be seen that LVEF actually reflects the ratio of changes in left ventricular end-diastolic and end-systolic volumes and, therefore, receives a greater influence from volume loading. In actual clinical work, the LV ejection fraction should be understood and interpreted in the context of the patient’s clinical condition and cardiac lesion. For example, in patients with hypertrophic cardiomyopathy, where left ventricular hypertrophy results in a smaller left ventricular cavity, if the left ventricular end-diastolic volume is 60 ml, the end-systolic volume is 30 ml, and the volume per beat is 30 ml, the LVEF is 50%. In patients with moderate to severe mitral regurgitation, if the LV end-diastolic volume is 150 ml, the end-systolic volume is 75 ml, and the volume per beat is 75 ml, the LVEF is 50%. Clinically, the LVEF is 50%, but the volume per beat does vary considerably, so the latter may be less symptomatic than the former. In addition, LV ejection fraction may not be an adequate indicator of LV myocardial contractile performance, and patients with moderate to severe mitral regurgitation may already have abnormal LV contractile performance when they present with a nominally normal LV ejection fraction of 60%. Theoretically, an ideal index of myocardial contractile performance should be independent of cardiac anterior and posterior loads, but no such ideal index has been found clinically. To compensate for the deficiencies of LV ejection fraction, more reliable indices for evaluating LV myocardial systolic function, such as volume per beat, cardiac output, cardiac index and LV myocardial contractile performance indices, such as dt/dp and Tei index, may be available.