Optimal loading and maintenance regimens for amiodarone are undefined. Serial electrophysiologic testing was used in 25 patients with ventricular tachycardia to assess the adequacy of a 1-week oral loading regimen at 1,200 mg/day, to modify maintenance dosing at the conclusion of loading, and to evaluate the appropriateness of maintenance dosing after 2 months of therapy. During the loading period, highly significant (p less than 0.001) increases occurred in the AH interval (88 +/- 22 vs 120 +/- 31 ms), HV interval (49 +/- 10 vs 61 +/- 11 ms), AV nodal Wenckebach cycle length (390 +/- 92 vs 537 +/- 147 ms), ventricular refractory period (247 +/- 17 vs 276 +/- 23 ms), mean ventricular tachycardia cycle length (254 +/- 38 vs 298 +/- 52 ms) and return cycle length (294 +/- 55 vs 360 +/- 87 ms). Ventricular tachycardia inducibility decreased in only a minority of cases, and when observed in association with a more than 10% increase in ventricular refractory period, resulted in a lower maintenance dose. After 2 months of maintenance therapy no additional change occurred in any of these parameters except for an increase in ventricular tachycardia cycle length (298 +/- 52 vs 330 +/- 65 ms, p less than 0.017). Ventricular tachycardia inducibility again showed no consistent response. It is concluded that patients can be discharged after 1 week of therapy with oral amiodarone loading at 1,200 mg/day and that maintenance dosing modified by electrophysiologic assessment results in steady perpetuation of the cardiac amiodarone effect, as indicated by the time course of change in electrophysiologic variables consistently affected.