The purpose of the present study was to establish the relationship of left ventricular end-systolic volume vs. mean systemic pressure in variously afterloaded beats in a group of healthy, young, men (n = 6, age 24 +/- 0.9 years). The relationship was expressed by the slope (Emax) of the line connecting pressure-volume co-ordinates and its extrapolated intercept (Vd) of the volume axis. The slope was calculated by linear regression of mean systemic arterial pressure (mean SAP, measured by catheter in the radial artery) vs. end-systolic left ventricular volume (ESV, estimated from cross-sectional, 4-chamber echocardiographic images). Recordings were obtained at resting, reduced (nitroglycerin infusion), and elevated (metaoxedrin infusion) blood pressure. Individual Emax values ranged from 1.05 to 2.01 mmHg ml-1; Vd was consistently found to be negative, ranging from -4.7 to -54.8 ml. All individual relations were statistically significant (P less than 0.05 to P less than 0.001). Group values were Emax = 1.27 +/- 0.25 (SE) mmHg ml-1, Vd = -43.3 +/- 7.5 (SE) ml, and Emax indexed for body surface area, Emax ind = 2.54 +/- 0.49 (SE) mmHg ml-1 m-2. We further examined the validity of proposed optimal relations among Emax, heart rate (HR) and systemic resistance (Rs): Emax/HR = Rs, and among ejection fraction (EF), EDV and Vd: EF = 0.5 (1 - EDV/Vd). For the group Emax/HR = 0.023 +/- 0.003 and Rs = 0.016 +/- 0.004 (mmHg ml-1 min-1), i.e., a deviation from equivalence of 30% (P less than 0.001). EF (= 0.72 +/- 0.02) deviated by 18% (P less than 0.001) from its proposed optimum (0.5 (1 - Vd/EDV) = 0.61 +/- 0.06).