In many countries, cardiovascular diseases are the main cause of death. Since the whole blood circulation depends on the heart, it cannot rest in order to recover as most of other muscles can. In some patients with not so severe damages in the myocardium, a rotary blood pump (RBP) may temporarily unload the native heart and can permit the recovery of the cardiac function. Since both implantation and withdrawal of the RBP are invasive procedures, the recovery should be detected with accuracy before weaning of the RBP. Therefore, the objective of this study is to estimate the cardiac function of assisted hearts using the maximum ventricular elastance Emax which is a cardiac function index representing the left ventricle contractility. Conventionally, the index Emax has been estimated using left ventricle pressure (LVP) and volume (LVV) during multiple cardiac cycles and under different loads. The two main problems of this method are that a precise measurement of LVV is invasive, and that induced changes in load should be avoided in cardiac patients. The single beat methods have the advantage that can be used with no changes on left ventricle load. In particular, the parameter optimization method (POM) permits Emax also to be calculated also using flow instead of volume in the case of non-assisted hearts. The conventional estimation of Emax and also the estimation using the POM with LVP and LVV had already been validated under the assistance of the RBP. This study shows that, in particular in cases with non-opening of the aortic valve, Emax can also be estimated by the POM using pump flow instead of LVV.