Controversy exists regarding the relative safety of intravenously administered lidocaine and procainamide to patients with acutely impaired hemodynamics. Accordingly, their effects were studied in 15 such patients, 14 with acute myocardial infarction and one with cardiomyopathy and severe congestive heart failure. All had elevated levels of pulmonary capillary wedge pressure (greater than 15 mm Hg) and/or low cardiac index (less than 2.5 liters/min/m2). Patients were given lidocaine, a 100 mg bolus followed by a 3 mg/min infusion and, after at least a 30 minute recovery period, procainamide, a 100 mg bolus over 2 minutes followed by a 20 mg/min infusion for 20 to 25 minutes. Hemodynamic measurements were compared early and late in the infusion of each drug. Small, clinically insignificant differences were observed in the hemodynamic responses to the drugs, and no clinically significant deterioration occurred with either. Conventional therapeutic doses of intravenous procainamide can be administered by this regimen, to patients with acute myocardial infarction complicated by cardiac failure or low cardiac output, without producing deleterious hemodynamic effects.