The short-term effects of dopexamine hydrochloride, a new synthetic adrenergic agent with predominant beta 2-adrenergic and dopaminergic properties, were studied in nine patients with inadequate cardiac output during the course of an episode of respiratory failure associated with lung infection. Dopexamine at doses up to 5 microgram/kg/min had no significant effect on arterial pressure or cardiac filling pressures, but increased cardiac index from 2.0 +/- 0.2 to 2.6 +/- 0.2 L/min.m2. Left ventricular stroke work increased from 17.3 +/- 15 to 22.1 +/- 2.4 g.m/m2 (p less than 0.01) and systemic vascular resistance index decreased from 3,792 +/- 1,035 to 2,194 +/- 823 dynes.s.cm5.m2 (p less than 0.01). The increase in cardiac output was in part related to an increase in heart rate from 91 +/- 6 to 102 +/- 7 beats/min. Under a mean inspiratory oxygen fraction of 0.48, the PaO2 decreased from 105 +/- 12 to 91 +/- 11 mm Hg (p less than 0.05) as venous admixture increased from 15.8 +/- 1.0 to 18.1 +/- 1.4 percent (p less than 0.05). Accordingly, the combination of inotropic, afterload-reducing and renal vasodilating effects of dopexamine can be useful acutely to increase cardiac output in critical conditions. However, its administration can be limited by a dose-related increase in heart rate. Dopexamine, like other catecholamines, alters blood oxygenation and increases venous admixture.