Three measures of left ventricular (LV) performance derived from pressure (P)-volume (V) loops have been proposed: the end-systolic P-V (PES-VES) relation, the stroke work-end-diastolic V (SW-VED) relation, and maximum dP/dt-VED (dP/dtmax-VED) relation. We evaluated the variability of repeated determinations, and inotropic and load sensitivity of these relations in conscious dogs. LVV was determined from three orthogonal LV diameters measured by sonomicrometry. Three to six sets of variably loaded P-V loops were generated by transient caval occlusions before and again after increasing inotropic state by infusing dobutamine (6 +/- 1 microgram/kg/min, mean +/- SD) and after increasing PES by 49 +/- 17 mm Hg with phenylephrine following autonomic blockade. The slope (MSW) of the SW-VED relation was the least variable at constant inotropic state (coefficient of variation, 4 +/- 3%) compared with the slope (EES) of the PES-VES relation (8 +/- 3%) or the slope (dE/dtmax) of the dP/dtmax-VED relation (11 +/- 6%, p less than 0.05). The extrapolated volume-axis intercept of the SW-VED relation was much less variable than the intercepts of the PES-VES or dP/dtmax-VED relations. MSW, EES, and dE/dtmax all increased (p less than 0.05) in response to dobutamine. The extrapolated volume-axis intercepts of the PES-VES and dP/dtmax-VED relations increased with dobutamine, whereas the volume intercept of the SW-VED relation was unchanged. MSW had the smallest increase in response to dobutamine (124 +/- 22% of control) compared to EES (178 +/- 67% of control) and dE/dtmax (211 +/- 68% of control, p less than 0.05). The position of the PES-VES relation, quantified as the VES at PES = 100 (V100), showed less variability (2 +/- 1%) than the slope of the PES-VES relation (8 +/- 3%, p less than 0.05). V100 decreased from 30.8 +/- 17.4 to 26.7 +/- 13.7 ml during dobutamine (p less than 0.05). After phenylephrine, EES, MSW, and dE/dtmax decreased by less than 10% (p = NS). The PES-VES relation shifted to the left with this increased afterload and V100 decreased by 3.2 +/- 1.5 ml (p less than 0.05), whereas the position of the SW-VED and dp/dtmax-VED relations were relatively unchanged.(ABSTRACT TRUNCATED AT 400 WORDS)