Histologically, haematoxylin and eosin (H&E) and Masson's trichrome staining detected that a moderate to severe myocardial fibrosis was developed in Smad3 WT‐db/db mice as well as Smad3+/− db/db mice, which was blunted in db/db lacking Smad3 (Smad3 KO‐db/db Figure 2A,C). Here, SMAD3 is linked to Myocardial fibrosis.