Precise assessment of left ventricular (LV) contractility during veno-arterial extracorporeal membrane oxygenation (VA-ECMO) support is crucial. However, changes in loading conditions may mask changes in LV function when assessed with load-dependent parameters. We compared end-systolic elastance (Ees, mm Hg/ml), the reference load-independent parameter of LV contractility, with LV ejection fraction (LVEF) in two patients. The first patient was a 54-year-old patient supported with femoro-femoral VA-ECMO for a cardiogenic shock. Afterload was calculated by using arterial elastance (Ea, mm Hg/ml). Although Ees near doubled from day 0 to day 3, no significant change was observed in LVEF. The second patient was a 61-year-old patient supported with femoro-femoral VA-ECMO for severe heart failure complicated with sepsis. We retrospectively showed that discrepancy between LVEF and Ees resulted from changes in LV-arterial coupling. We concluded that LVEF may be misleading in the assessment of LV function during VA-ECMO for heart failure.