A new cardioselective beta 1-adrenergic receptor agonist xamoterol (Corwin) has been developed for the treatment of heart failure. To study the acute hemodynamic effects of xamoterol, 24 patients, 39-70 years old, with mild-to-moderate postinfarction left ventricular dysfunction entered a double-blind, between-patient comparison of a single 5-minute intravenous infusion of xamoterol (0.2 mg/kg) and placebo. The acute hemodynamic effects of xamoterol were measured at rest and during two multistaged symptom-limited supine bicycle exercise tests (Ex-T), a control Ex-T followed by an Ex-T with either xamoterol or placebo. Compared with placebo, xamoterol significantly increased left ventricular contractility (Vmax and positive [+] dP/dt) and enhanced relaxation (dP/dt- and time constant relaxation) at rest and at the 25% and 50% levels of maximum exercise. The heart rate, the frequency and time to onset of anginal symptoms, the magnitude of exercise-induced ST segment depression, the left ventricular end-diastolic and peak systolic pressures, the mean pulmonary artery pressures, the cardiac index, the left ventricular stroke-work index, and the epinephrine and norepinephrine plasma levels at rest and during exercise did not differ significantly between placebo xamoterol groups. Thus, xamoterol can be a useful addition for the treatment of left ventricular dysfunction because of long-term ischemic heart disease.