The purpose of the present study was to determine (1) whether simvastatin (SV) modifies the rate-dependent conduction time and refractoriness of the atrioventricular (AV) node and (2) how it can change the protective mechanism of the AV node during atrial fibrillation (AF). Predefined stimulation protocols were applied to detect the electrophysiological parameters of the AV node, including atrial-His conduction time, effective refractory period (ERP), functional refractory period (FRP), concealed conduction, excitable index, and fatigue in two groups of isolated, perfused rabbit AV nodal preparations (N=16). The stimulation protocols (fatigue, recovery) were carried out during control and in the presence of SV (0.5, 0.8, 3, and 10 μM). Simulated AF was executed in a separate group (N=8), and specific indexes, including H-H mean, zone of concealment (ZOC), and concealed beats were recorded. SV, in a concentration-dependent manner, prolonged ERP, FRP, and Wenckebach cycle lengths. It (10 μM) significantly increased fatigue and the excitable index. In addition, SV elicited prolongation of ZOC and H-H mean at 3 and 10 μM. SV-evoked prolongation of nodal refractoriness and concealed conduction caused rate-dependent ventricular slowing effects during AF. The ability of simvastatin to decrease the excitable gap by its heterogeneous effects on nodal dual pathways proposes its protective role in AF.