Viewing canine left ventricular performance through the pressure-volume (P-V) window, I proposed a new index of ventricular contractility (Emax: end-systolic P-V ratio or maximum elastance) in my doctoral thesis at the University of Tokyo in 1969. After I joined Dr. Kiichi Sagawa (deceased in 1989) at Johns Hopkins University, we firmly established the Emax concept during 1971-1978. The concept was extended to derive the systolic P-V area (PVA) as a new measure of the total mechanical energy generated by ventricular contraction in 1978. Experiments have revealed that PVA closely correlates with cardiac oxygen (O2) consumption (VO2) under various loading conditions at a constant Emax, the VO2-PVA relation changes its elevation with Emax, and the O2 costs of PVA and Emax characterize the mechanoenergetics of cardiac contraction under various normal and abnormal conditions in an innovative manner (Suga: Physiol Rev 70: 247-277, 1990). Emax and PVA can also evaluate the ventriculo-arterial hydraulic and energetic matching in normal and failing hearts. Emax and PVA have thus widely opened the P-V window to the extent that human and animal normal and failing cardiac performance can be characterized in a physiologically sound manner.