Introduction: Electrical heterogeneity in the atria has been consistently linked with the initiation and perpetuation of atrial fibrillation (AF). The present model-based study investigated the contribution of action potential duration (APD) heterogeneities in the left atrium (LA) and right atrium (RA) on the perpetuation of the reentrant activity during AF. Methods: A computer model with a geometry based on computed tomography of AF patients and a Courtemanche atrial cellular model was implemented. Self-terminated AF episodes were initiated via ramp pacing in a model with modified channel conductance, homogeneous tissue and 4:1 anisotropy ratio. Once AF was observed, random patchy heterogeneities with shorter APD were separately introduced in the LA and the RA. Percentage of heterogeneities was progressively increased from 20% to 80% of each atrium size (characteristic length scale of patches was 7.5mm). For each simulation, the following values were assessed: average AF duration, the number of sustained AF episodes (lasting more than 50s), number of wave-fronts (#WF) and AF cycle length (AFCL). The results were averaged across the atria surface over 130 simulations (26 AF initial conditions and 5 random localizations of heterogeneities). Results: For the model with no heterogeneities, #WF was 6.82±3.67, AFCL 278±52ms and the average AF duration 15.42±9s. For low percentage of heterogeneities there were no significant differences between RA, LA and the model with no heterogeneities. For high percentage of heterogeneities the results showed that a significant right-to-left atrial APD gradient was associated with more sustained AF episodes, longer duration, higher #WF and shorter AFCL compared to the left-to-right APD gradient (sustained AF episodes: 95% vs. 52%, p<10-4; duration: 48±9s vs. 32.8±21s, p<0.05; #WF: 11.72±3.3 vs. 9.7±3.1, p<10-4; AFCL: 209±69ms vs. 223±64ms, p<0.05). Conclusion: High inter-atria differences in APD significantly affect the dynamics and the duration of the reentrant activity. Our findings are in line with previous studies reporting the right atrium as the dominant driver in some persistent AF cases.