SMAD3 and Myocardial fibrosis: The TGF-β1 and P-Smad2/Smad3 protein expressions were markedly higher in HFpEF rats than in WKY rats (for all, P < 0.01 or 0.001, Figures 5J,L), and TGF-β1 protein expressions were also higher than in SHR rats (for all, P < 0.01), suggesting that activating the TGF-β1/Smads pathway might regulate fibroblast activation and collagen synthesis, thereby promoting myocardial fibrosis in HFpEF rats.