The goal of this study was to measure the effective refractory period (ERP), the conduction velocity (CV) and the wavelength (WL) after cardioversion in patients with persistent atria] fibrillation (AF) and to determine the effects of the adenosine triphosphate sensitive potassium channel (KATP) opening agent, nicorandil, on those parameters in patients with persistent AF. METHODS: Patients with AF underwent elective cardioversion followed by measurement of ERP and CV before and after administration of nicorandil. Parameters were measured again one week later, and the ERP and the CV was used to calculate WL. RESULTS: ERP was significantly shorter immediately after termination of AF than at the 1-week time point (193.4 vs. 228.7 msec p < 0.01). While there was no significant difference in ERP immediately after termination of AF when comparing measurements taken before and after the administration of nicorandil, ERP at the 1-week time point was shorter after nicorandil administration than before nicorandil administration (193.4 vs. 191.4 msec, n.s.; 228.7 vs. 217.2msec, p < 0.01). Further, WL was higher at the 1-week time point after nicorandil administration than before nicorandil administration. CONCLUSIONS: These data indicate that the electrical remodeling that occurs after cardioversion is at least partially mediated by changes in KATP channel behavior. Further, the electrophysiologic properties, that is, nicorandil prolonging the WL, may be of benefit in reducing the recurrence rate of AF.