In the treatment of refractory ventricular tachyarrhythmias antiarrhythmic drugs must sometimes be combined. An electrophysiologically appropriate combination is lignocaine and procainamide and, when needed, a β-blocking agent. The hemodynamic effects of this treatment were studied in 6 patients in the acute phase of myocardial infarction. After a control period, an infusion of lignocaine was started and 1 h later procainamide/placebo was added in a double-blind system and finally also practolol/placebo. The drugs were given intravenously in ordinary doses. Hemodynamics were studied by bedside catheterization. During triple treatment heart rate and aortic pressures fell significantly whereas right atrial mean pressure increased compared to the control period. Stroke volume, cardiac output and pulmonary artery pressures were unchanged. Most of the changes appeared when practolol was added. Following the procainamide injection a transient fall in aortic pressures was noted. Lignocaine gave no hemodynamic effects. The number of ventricular premature beats was reduced in all patients and no patient had ventricular tachycardia during treatment. In these patients it was possible to combine lignocaine, procainamide and practolol in the acute phase of myocardial infarction. However, 3 patients developed hypotension, 1 sinus bradycardia and 1 had a short run of nodal tachycardia. It is concluded that this kind of combined treatment, because of its potential risks, should be restricted to critical clinical situations and then it ought to be hemodynamically controlled.