Obesity has been demonstrated to be linked to atrial fibrillation (AF) with atrial enlargement and tissue fibrosis. Long-term high calorie intake is the main reason for the prevalence of obesity. To investigate the possible causes of AF, such as chronic high-fat diet (HFD), and to identify the underlying mechanisms, the present study analyzed a variety of structural and gap junctional electrophysiological alterations in the atria of female rats fed an HFD. After consistent HFD feeding of female rats for 12 weeks, hematoxylin and eosin (H&E) and Masson's staining, RT-qPCR, western blotting, immunofluorescence and TUNEL staining were performed. In our study, approximately 3/5 of the HFD-fed rats (HFD-OB, n= 13) displayed a significant increase in body weight, while the other 2/5 did not (HFD-NOB, n= 8). In addition, the atrial weight of the HFD-OB and HFD-NOB rats was markedly heavier, as compared to the rats fed a normal diet (CT, n= 20). According to the plasma lipid levels, both HFD-OB and HFD-NOB rats exhibited dyslipidemia. Furthermore, H&E staining revealed broadened interstitial space and myocyte disarray in atria of the HFD-fed rats (ie, HFD-OB and HFD-NOB rats). Expression levels of atrial fibrosis relevant factors, transforming growth factor-β1 and matrix metalloproteinase-2, were significantly upregulated in the HFD-fed rat atria. In addition, we found a gap junction remodeling with distinct alterations in expression and distribution of connexin 40 (Cx40) and Cx43 in the HFD-fed rat atria. Moreover, a modest increase in apoptotic cell death in both the HFD-OB and HFD-NOB rat atria was detected. Taken together, our findings demonstrated that the impact of chronic HFD on atria displayed in the diet-induced obese rats was observed in HFD-fed rats in the absence of obesity as well.