The intravenous administration of 3 or 5 mg of glucagon to 13 patients with heart disease resulted in a statistically significant increase in heart rate, cardiac index, stroke power index, mean rate of left ventricular ejection, and maximum rate of rise of left ventricular pressure, whereas systemic vascular resistance declined. A moderate increase in mean stroke volume index and stroke work index and a slight fall in left ventricular end-diastolic pressure also occurred, although these changes were not statistically significant. The increase in cardiac index averaged 19%, with nine of the patients demonstrating an increase exceeding 10% of their respective control value. These effects of glucagon generally reached a maximum within 15 min after drug administration and also were of short duration.Positive inotropic and chronotropic effects of glucagon were observed in most but not all of these patients. In addition, the magnitude of these effects varied considerably among patients; the variation, however, did not appear to be related to the severity or duration of the heart disease.In eight patients, the infusion of isoproterenol produced greater increases in cardiac index and decreases in left ventricular end-diastolic pressure than glucagon did.Although the effect of glucagon was short, the frequent improvement in hemodynamics which occurred in the absence of significant side effects, notably arrhythmias, indicates that the inotropic actions of this agent may be useful under certain clinical conditions.