Aims To study, using simulation, the spectral characteristics of different patterns of atrial fibrillation (AF) at high spatial resolution. Dominant frequency (DF) and organization index (OI) maps have been used to approximate the location of the focal source of high frequency during AF events. Methods and results A realistic three-dimensional model of the human atria that includes fibre orientation, electrophysiological heterogeneity, and anisotropy was implemented. The cellular model was modified to simulate electrical remodelling. More than 43 000 electrograms were calculated on the surface, and were processed to reconstitute the DF and OI maps. Atrial fibrillation episodes were triggered by a source of transitory and of continuous activity (both with a cycle length of 130 ms) in five different locations. The maps obtained during the AF events triggered by transitory foci did not show areas with high DF or OI values. When continuous foci were applied, the DF maps show ample zones with high values in the atrium where the focus was applied; while OI maps display smaller areas with high values, always within the areas of high DF and, in three of five locations, this high-value area was located at the site of focus application and at the nearby area. In the other two locations, the area presenting the highest OI values is small and located at the site of focus application, which allowed its precise localization. Conclusion Organization index maps provide a better approximation than DF maps for the localization of ectopic sources of high frequency and continuous activity during episodes of simulated AF in remodelled tissue.