This summarizes my 25 year long research carried out for a better understanding of the systolic function of the heart. My research began with the discovery of Emax (end-systolic maximum elastance or pressure volume ratio) as an index of ventricular contractility on the basis of the time-varying elastance model of the left ventricle. The same time-varying elastance model evolved PVA (systolic pressure-volume area) as a measure of the total mechanical energy generated by ventricular contraction. We have found experimentally that both Emax and PVA closely correlate with myocardial oxygen consumption and proposed that the oxygen costs of Emax and PVA characterize the abnormality of cardiac mechanoenergetics under various pathophysiological conditions.