Intravenous glucagon, in doses of 2.5-15 mg/hour, was administered to 50 patients for periods of 1-7 days. Forty patients had either intractable heart failure or cardiogenic shock or both; the remaining 10 had less severe heart disease. In all patients glucagon was added to conventional therapy. Twenty-two of the 40 with very severe heart failure showed a clinical improvement, and 18 were discharged from the hospital; 16 of the 18 patients who did not respond died in the hospital. Only two of the 10 with less severe heart disease improved with glucagon but all could be discharged from the hospital. Glucagon did not initiate or aggravate a tendency to arrhythmias in any of the 17 patients with acute myocardial infarction. In two patients with bradycardia and cardiac failure due to beta-adrenergic blocking drugs, glucagon increased heart rate and there was clinical improvement in heart failure. However, there was no effect in two patients with digitalis-induced nodal bradycardia and heart failure. Nausea was the most troublesome side effect and this could usually be controlled by intramuscular prochlorperazine (Stemetil) which was given routinely before the infusion in all except postoperative patients and repeated as required during the infusion. The results show that glucagon has a definite place in the management of patients with severe heart failure when used as an adjunct to conventional therapy.