The left ventricular systolic pressure-volume diagram has been established before and after infusion of Nitro-prusside, Angiotensin and over post-extrasystolic potentiation on 33 patients, by the simultaneous measure of the aortic pressure and the left ventricular volume. In every case left ventricular dp/dt max. and (dp/dt/Pt) max. have been measured before and during post-extrasystolic potentiation, and in 16 cases after vasomotor therapy. The end-systolic left ventricular pressure-volume ratio appears to be independent of loading modifications--more than dp/dt max. and (dp/dt/Pt) max.--and on the opposite to be a good index of inotropic state alterations.