Time course of pressure/volume ratio of the left ventricle in systole has been proposed as a good index of its pumping properties; the ratio is an approximately steady function of time with its time course almost un-altered by changes in left ventricular end-diastolic volume (preload) and arterial loading conditions (afterload). It is the purpose of the present investigation to compare the ratio in a positive inotropic state with a control in experiments on the dog. The results indicate that the maximum value of the ratio in systole is increased and the time course is shortened by positive inotropism (stimulation of the left stellate ganglion), but that the contour of the time course is approximately unchanged by positive inotropism.