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Left ventricular diastolic pressure-circumference curves were determined in 13 dogs, during stepwise hemorrhage and transfusion of blood. The linearity and small amount of scatter in the pressure-circumference curves obtained during control circumstances is evidence that elasticity rather than viscosity or inertia is the dominant determinant of the curve. Coincident with the slow infusion of epinephrine the distensibility increased. The importance of viscosity and inertial effects in the myocardial wall may also have increased, as evidenced by the increased scatter of the pressure-circumference graph. The magnitude of the change in distensibility observed was great enough to produce large changes in ventricular performance at a given filling pressure.

No abstract