Fenoterol (a selective beta-2-adrenergic drug) was given intravenously (2 mcg/kg body weight/15 min) to 7 normotensive patients after open-heart surgery in order to study the cardiovascular and respiratory effects. A marked cardiovascular effect was seen without changes in venous or arterial pressure. The increased heart rate (46%) was of sinus or atrial origin; no ventricular arrhythmias were seen. The cardiac index rose by 91%; left and right ventricular stroke work increased by 26% and 54% respectively; systemic and pulmonary vascular resistance decreased by 31% and 23% respectively; arterial oxygen tension decreased from 264 to 205 mm Hg; oxygen consumption rose 31%. No changes occurred in respiratory dynamics, in the total respiratory system of patient and tubes. The cardiovascular effect of fenoterol, without a corresponding increase in end-diastolic filling pressure and resistance against systolic ejection of the left ventricle, as well as the absence of ventricular arrhythmias, indicate that the drug may be useful as a supplement to other sympathomimetic compounds in normal use.