Using a diagram representing the relationship of intraventricular pressure and conductance, we determined ventricular efficiency from the weighted relationship between the area encompassed by the loop (the stroke work) and the total area surrounded by the end-diastolic curve, the systolic segment of the diagram, and the end-systolic line. The basic concept underlying this calculation stems from the linear relationship between consumption of oxygen by the heart and the total area discussed above, a relationship already well established in the literature. In five animals investigated under control conditions, values ranged, as expected, from 17.5 to 30.6% (average 21.78%, SD 5.06). They showed a significant increase (P less than 0.05) after an inotropic maneuver (range 19.9-40.0%, average 31.17, SD 7.43). An attractive feature is that the diagrams need not be calibrated in absolute terms. The procedure can be easily applied during routine cardiac catheterization to obtain complementary information (ventricular efficiency) which is of value in the evaluation of cardiac performance.