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SUMMARY We performed intracardiac electrophysiologic studies in 33 patients with recurrent ventricular tachycardia. Nineteen patients underwent one, 10 patients two, and four patients three serial electrophysiologic studies. Ventricular tachycardia was successfully induced in 83% of the patients, and pacing methods were successful in terminating tachycardia in 71% of the studies, although pacing-induced acceleration of ventricular tachycardia occurred at least once in 36% of the studies. Seventeen of the 33 patients (52%) required a total of 24 external direct current cardioversions during study.In 21 patients a variety of antiarrhythmic drugs were given I.V. and attempts at ventricular tachycardia induction were repeated to assess prophylactic effects of the drugs. An acutely effective drug or combination of drugs was found in 15 of the patients (71%). Fourteen of the 15 were placed on chronic oral therapy with the effective agent and were followed for an average period of 8.1 months (range one to 33 months). In all 14 patients we could document complete (13 patients) or partial (one patient) long-term prophylaxis against ventricular tachycardia.We conclude that drug efficacy trials in patients with recurrent ventricular tachycardia using intracardiac pacing techniques is a rapid and accurate method of selecting effective long-term antiarrhythmic therapy.