The analysis of left ventricular end-systolic pressure-volume relationships in human beings has been hindered by the lack of a practical method of serial volume assessment and by an imprecise definition of end-systole. Modifications of the end-systolic relationship that have been used to circumvent these problems have included the use of single-point end-systolic pressure-volume ratios, the use of peak systolic pressure/minimum ventricular volume points for end-systolic points, and the use of end-ejection as a marker for end-systole. To assess the correlation between the parameters generated by these modifications with the slope (E(max)) and volume intercept (V(o)) of the end-systolic line as defined by Sagawa's model of time-varying elastance, simultaneous measurement of left ventricular pressure and gated radionuclide volume was made in 26 patients under various loading conditions and pressure-volume diagrams were constructed for each loading condition from 32 simultaneous pressure-volume coordinates. Two pressure-volume diagrams were recorded in 14 patients and three pressure-volume diagrams were recorded in 12 patients. E(max) and V(o) were determined in all patients from the slope and volume intercept of the isochronic pressure-volume line with the maximum time-varying elastance as described by Sagawa's model and were designated true E(max) and true V(o), respectively. True E(max) was subsequently correlated with three estimates of E(max) computed from a single-point end-systolic ratio (r = .76, SEE = 1.53, p < .001), from peak systolic pressure/minimum systolic volume points (r = .87, SEE = 0.67, p < .001), and from end-ejection pressure-volume points marked by peak negative dP/dt (r = .91, SEE = 0.57, p < .001). It is concluded that the parameters E(max) and V(o) of a time varying elastance model of the end-systolic pressure-volume relationship can be constructed for man with the use of simultaneous left ventricular pressure measurements and gated radionuclide ventriculography, and that true E(max) calculated by this method is reasonably approximated by single-point pressure-volume ratios and peak systolic and end-ejection measurements.