The linearity and sensitivity of the end-systolic pressure-volume (P-Ves) relation to the inotropic state of the left ventricle were investigated in 11 patients with coronary heart disease and one patient with congestive cardiomyopathy. To minimize autonomic reflex responses, propranolol, 0.15 mg/kg, and atropine, 1 mg, were administered i.v. at the beginning of the study. Three ventriculograms were performed: at rest, after oral isosorbide dinitrate, 10 mg (systolic pressure decrease 15 ⩾ mm Hg), and during infusion of methoxamine, 2 mg/min (systolic pressure increase ⩾ 10 mm Hg).The three points of the P-Vesrelation showed linearity (r⩾ 0.96). The relation between the slope k of the PVesrelation and the left ventricular ejection fraction at rest was best described by an exponential function (r= 0.94). The use of peak systolic pressure instead of end-systolic pressure showed equally good results. The intercept of the PVesline on the abscissa, which represents the theoretical end-systolic volume at zero pressure, was not related to the ejection fraction under control conditions. The P-Vesrelation in postextrasystolic beats was displaced toward the left (smaller end-systolic volumes) and became steeper.