Dobutamine, a new synthetic inotropic agent, was administered by intravenous infusion to 22 patients following open heart surgery. The dosage of dobutamine started from 2 mug/kg/min and was increased stepwise to 4, 6, and 8 mug/kg/min. Cardiac index increased from 2.54 +/- 0.13 to 3.11 +/- 0.19 and 3.50 +/- 0.22 L/min/m2 with 4 and 8 mug/kg/min, respectively. Heart rate increased from 87.6 +/- 2.9 to 96.4 +/- 2.3 and 108.9 +/- 3.2 beats/min with 4 and 8 mug/kg/min, respectively. Systolic and mean aortic pressure and systolic pulmonary arterial pressure were elevated from 126.0 +/- 3.8 to 144.6 +/- 6.0 mm Hg, from 91.8 +/- 2.7 to 96.2 +/- 3.2 mm Hg, and from 33.4 +/- 2.3 to 37.1 +/- 2.5 mm Hg with 8 mug/kg/min, while other pressures were unchanged. Mean left atrial pressure fell significantly from 15.9 +/- 0.6 to 14.8 +/- 0.7 mm Hg. Stroke volume index, stroke work index, and left ventricular work also increased. Premature ventricular beats were observed in only one patient during dobutamine infusion, but no other side effect was observed. We conclude that dobutamine is a potent inotropic agent which increases cardiac output without causing significant tachycardia or arrhythmias, and is useful for the treatment of patients following open heart surgery.