Cardiac output (CO) was measured before and during pressor-amine infusion in eight patients with septic shock and in seven patients with shock from myocardial infarction. Levarterenol bitartrate or metaraminol bitartrate infusion in sufficient dosage to maintain systolic blood pressures of 90 to 130 mm Hg increased the peripheral resistance in both groups. These pressor amines tended to raise the CO in patients with sepsis and lower it in those with myocardial infarction. Increasing the pressor-amine dosage for greater bloodpressure effect consistently lowered the CO, which suggests that blood-pressure support at low normal levels is hemodynamically preferable. In three cases, angiotensen amide produced lower CO's than equipressor doses of levarterenol.