Twenty-six patients had ventricular tachycardia initiated at control electrophysiologic study and had a repeat study during oral propafenone therapy. Ten patients had had sustained ventricular tachycardia, 6 cardiac arrest and 10 symptomatic, nonsustained ventricular tachycardia. Twenty-two patients had heart disease, 18 of whom had coronary artery disease. During propafenone therapy, ventricular tachycardia could not be initiated during programmed ventricular stimulation in 5 patients, and in 21 patients the cycle length of induced ventricular tachycardia increased from 246 +/- 42 ms at control to 355 +/- 96 ms (p less than 0.001). Seventeen patients were discharged with propafenone therapy and have been followed for a mean of 11 months. No symptomatic ventricular tachycardia recurred in the 5 patients without inducible ventricular tachycardia during drug treatment. Six of 12 patients with inducible ventricular tachycardia during the drug study have remained asymptomatic. In conclusion, propafenone substantially prolongs the cycle length of ventricular tachycardia, and initiation of ventricular tachycardia by programmed ventricular stimulation at drug study does not preclude a favorable clinical outcome.