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Introduction: Amiodarone is effective in preventing the recurrence of atrial fibrillation (AF) after cardioversion (CV). Dispersion of atrial refractoriness may be relevant to the generation of AF. We designed a study to determine the electrophysiologic effects of amiodarone in patients with previous early recurrence of AF after CV., Methods and Results: Fifteen patients with previous AF recurrence (without antiarrhythmic drugs) after CV (CV1) were selected for amiodarone therapy and repeat CV (CVamio). Prior to CV1, mean AF cycle length (AFCL) had been recorded at four atrial sites (right atrial appendage [RAA], distal coronary sinus [DCS], right atrial lateral wall [LAT], and interatrial septum [IAS]) and dispersion of AFCL had been calculated. These patients were treated with amiodarone and, prior to CVamio, AFCL was recorded at the four atrial sites as for CV1. Between CV1 and CVamio, AFCL increased at all atrial sites: 153 +/- 13 msec to 179 +/- 14 msec at RAA, 144 +/- 12 msec to 174 +/- 18 msec at DCS, 158 +/- 13 msec to 182 +/- 16 msec at LAT, and 161 +/- 18 msec to 181 +/- 17 msec at IAS. Dispersion of AFCL decreased from 24 +/- 10 msec at CV1 to 15 +/- 11 msec at CVamio (P = 0.01). The median time in sinus rhythm increased from 3.12 hours post CV1 to 28 days post CVamio, (P < 0.02)., Conclusion: Amiodarone causes a reduction in the dispersion of AFCL. This action may be relevant to the beneficial effects of amiodarone in patients with AF.