We assessed cardiac function by acute pressure loading with phenylephrine in 7 patients who had hyperdynamic sepsis and in 8 patients who had heart disease. All patients with sepsis had a positive Limulus lysate test, a septic focus, and a cardiac output (CO) greater than 6.0 L/min. Phenylephrine was given iv to elevate systolic arterial pressure by 30 mm Hg. Cardiac index (CI) and stroke index (SI) increased significantly in patients with hyperdynamic sepsis, whereas systemic vascular resistance index (SVRI) showed no change. In patients with heart disease, CI and SI decreased significantly, whereas SVRI increased significantly. The marked differences in response to phenylephrine by the two groups suggest lack of cardiac dysfunction in patients with hyperdynamic sepsis.