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Background: Much echocardiographic research into left ventricular (LV) function relies heavily onthe assumption: that LV systolic function can be described by the contractility index end-systolic elastance (Ees). It has been suggested that Ees can be simply calculated as the ratio between LV end-systolic pressure (ESP) to end-systolic volume (ESV). As based on pressure-volume loop analysis, this method relies on the fundamental assumption that the slope of the LV end-systolic pressure-volume relations intersects the volume axis at a negligible value and therefore can be approximated as zero, which however is controversial. We wished to critically test this assumption.Methods and Results: Pressure and volume data were obtained at baseline and after a load intervention with iv. nitroglycerin (NTG) in n=65 patients (age=67±9) undergoing coronary angiography and simultaneous echocardiography (LVEF=55±8%). The simplified Ees (EesSimp=baseline ESP/baseline ESV) was compared to the Gold Standard (GS) ratio obtained using delta pressure and volume values from baseline to post-NTG (EesGS=dESP/dESV). It was found that EesSimp correlated relatively poorly to EesGS (r=0.34; p=0.04) and that the two methods provided values of volume axis intersect that substantially differed from the assumed zero value (EesSimp V0 : mean -7.0mL vs EesGS V0 : -62.2mL).Conclusion: The very popular systolic index ESP/ESV agrees relatively poorly with Gold Standard LV contractility as the volume axis intercept is non-negligible.