A new index to assess left ventricular (LV) function in patients implanted with continuous flow left-ventricular assist devices (LVADs) is proposed. Derived from the pump flow signal, this index is defined as the coefficient (k) of the semiloga-rithmic relationship between pseudo-ejection fraction (pEF) and the volume discharged by the pump in diastole, (V d). pEF is defined as the ratio of the pseudo-stroke volume (pSV) to V d. The pseudo-stroke volume is the difference between V d and the volume discharged by the pump in systole (V s), both obtained by integrating pump flow with respect to time in a cardiac cycle. k was compared in-vivo with others two indices: the LV pressure-based index, M TP, and the pump flow-based index, I Q. M TP is the slope of the linear regression between the triple-product and end-diastolic pressure, EDP. The triple-product, TP LV SP.dP/dt max. HR, is the product of LV systolic pressure, maximum time-derivative of LV pressure, and heart rate. I Q is the slope of the linear regression between maximum time-derivative of pump flow, dQ/dt max, and pump flow peak-to-peak amplitude variation, Q P2P. To test the response of k to contractile state changes, contractility was altered through pharmacological interventions. The absolute value of k decreased from 1.3540.25 (baseline) to 0.6850.21 after esmolol infusion. The proposed index is sensitive to changes in inotropic state, and has the potential to be used clinically to assess contractile function of patients implanted with VAD.