Experimentally observed differences in the action potential (AP) properties between the left (LA) and right (RA) atria are believed to be important in maintaining reentrant sources during atrial fibrillation. We incorporate AP models for single LA and RA cells, as well as major intra- and interatrial conduction pathways, into a 2D atrial tissue model and study the role of tissue heterogeneity in global interactions between reentrant spiral waves in both atria. Our simulations show that shorter AP refractoriness in the LA translates into a shorter period of spiral rotation, and as a result, reentry in the LA dominates the overall excitation patterns in the atria.