In order to evaluate its hemodynamic actions, tocainide, a new orally effective antiarrhythmic drug, was given intravenously over a 15 minute period to 12 patients with compensated left ventricular dysfunction. Doses were 0.5 (4 patients) or 0.75 (8 patients) mg/kg/min. Hemodynamics and drug plasma concentrations were measured at the end and 15 minutes after the end of the infusion. Tocainide infusion produced small but statistically significant increases in the pulmonary and systemic vascular resistance, aortic and pulmonary arterial pressure, and left and right ventricular end-diastolic pressure. There was no significant change in left ventricular dp/dt, heart rate, or cardiac index. In patients with compensated left ventricular dysfunction, tocainide produces a small rise in vascular resistance and arterial pressure. Overall cardiac function is maintained with a small increase in left ventricular end-diastolic pressure.