During persistent atrial fibrillation, cardiac tissue undergoes electrophys-iological and structural remodeling. Fibrosis in the atrial tissue has an important impact on the myocyte action potential (AP) and its propaga-tion. The objective of this work is to explore the effect of heterogeneities present in the fibrotic tissue on the intracardiac electrogram (EGM). Hu-man atrial myocyte and fibroblast electrophysiology was simulated using mathematical models proposed by Koivumäki et al. representing electri-cal remodeling under peAF as well as a remodeling due to the paracrine effect of the transforming growth factor β1 (TGF-β1). 2D tissue simula-tions were performed using the monodomain approach and EGM forward calculations with the infinite conductor approximation. Furthermore, we varied the density of fibrosis (10%, 20%, 40%) present in a circular re-gion of 2cm diameter. We also varied the ratio of myocytes coupled to myofibroblasts vs. collagen in fibrotic elements (0%-100%, 25%-75%, 50%-50%, 75%-25%, 100%-0%). Results show that increasing the fibro-sis density changes the reentry dynamics from a functional to an anatom-ical reentry due to a block of conduction in regions with high fibrosis density (40%). Higher densities of fibrosis (40%) had a more homoge-nous distribution of Shannon entropy values inside the fibrotic region. EGM morphology was affected by the ratio of myofibroblasts vs. colla-gen. For low myofibroblast ratios (<50%), the mean duration of the ac-tive segments inside the fibrotic region were shorter (43.8 ms, 61.48 ms and 45.83 ms for 10%, 20% and 40% of fibrosis correspondently) com-pared to higher myofibroblast ratios (45.66 ms, 62.24 ms, 48.09 ms for 10%, 20% and 40% of fibrosis correspondently). Our results show that fibrosis arrangement can alter the dynamics of reentry and EGM mor-phology.