Isoxsuprine, a peripheral arteriolar vasodilator, was given to 12 patients with congestive heart failure. Cardiac index increased up to 31 percent; pulmonary artery wedge pressure fell by as much as 33 percent; mean arterial pressure fell by 17 percent; mean pulmonary artery pressure fell by 29 percent; systemic pulmonary vascular resistance fell by 37 percent; and pulmonary vascular resistance fell by 33 percent. All patients showed clinical improvement in the signs and symptoms of congestive heart failure during the three-hour observation period. This initial report documents the short-term salutary effects of isoxsuprine in congestive heart failure. The long-term efficacy of the drug remains to be evaluated.