Objective To investigate the effect of Vericiguat on myocardium fibrosis induced by Ach-CaCl2 in rats with atrial fibrillation (AF) and its mechanism. Methods Forty SD rats were randomly divided into sham group, AF group, AF+Vericiguat group and AF+Vericiguat+SRI-011381 (an activator of TGF-β signaling pathway) group, with 10 rats in each group. The AF rat model was prepared by injecting Ach-CaCl2 mixed solution into the tail vein. After successful modeling, Vericiguat and SRI-011381 were given intervention, and the same amount of vehicle was given to sham group. The duration of AF was recorded by electrocardiogram. HE and Masson staining were used to detect myocardial tissue injury and fibrosis. The level of hydroxyproline (Hyp) in myocardial tissue was detected by alkaline hydrolysis method. Immunohistochemistry was used to detect the expression of collagenⅠ and collagenⅢ in myocardial tissue. The protein expression levels of transforming growth factor-β1 (TGF-β1), p-Smad2, Smad2, p-Smad3 and Smad3 in myocardial tissue were detected by western blot. Results Compared with sham group, the AF group exhibited more severe myocardial tissue damage and fibrosis in rats, the AF duration and Hyp level in myocardial tissue were significantly increased (P＜0.05), and the protein expression levels of collagenⅠ, collagenⅢ, TGF-β1, p-Smad2/Smad2 and p-Smad3/Smad3 in myocardial tissue were significantly increased (P＜0.05). Compared with AF group, the degree of myocardial tissue injury and fibrosis in AF+Vericiguat group was significantly reduced, the AF duration and Hyp level in myocardial tissue were significantly decreased (P＜0.05), the protein expression levels of collagenⅠ, collagenⅢ, TGF-β1, p-Smad2/Smad3 and p-Smad3/Smad3 in myocardial tissue were significantly decreased (P＜0.05). However, combined intervention with SRI-011381 could significantly inhibit the improvement of Vericiguat on myocardial fibrosis of AF rats. Conclusion Vericiguat can ameliorate Ach-CaCl2 induced myocardial fibrosis in AF rats, the mechanism of which may be achieved by inhibiting TGF-β signaling pathway transduction