isovolumic and auxovolumic constants of cardiac relaxation in evaluating its inotropism the left ventricular pressure curve was registered in experiments on isolated guinea pig heart performing external work an analysis of initial diastolic portion of the curve in logarithmic scale has revealed for the first time that the time course of the pressure fall is accelerated during transition from isovolumic to auxovolumic phase the constant of pressure fall rate in auxovolumic phase acpfr has been approximately 15fold higher than isovolumic constant the former also changed significantly more than the latter one during elevation in ca2 perfusate concentration or egta addition a parallel reduction in acpfr and rate of left ventricular filling during egta addition was observed in special experiments with elimination of left atrium distension thus inotropic changes in myocardial relaxation seem to determine left ventricular filling rate