This study examined the effect of tanshinoneⅡA (TSNⅡA) on the cardiac fibrosis induced by transforming growth factor β1 (TGF-β1) and the possible mechanisms. Cardiac fibroblasts were isolated from cardiac tissues of neonatal Sprague-Dawley (SD) rats by the trypsin digestion and differential adhesion method. The cells were treated with 5 ng/mL TGF-β1 alone or pretreated with TSNⅡA at different concentrations (10–5 mol/L, 10–4 mol/L). Immunocytochemistry was used for cell identification, RT-PCR for detection of the mRNA expression of connective tissue growth factor (CTGF) and collagen type Ⅰ (COLⅠ), Western blotting for detection of the protein expression of Smad7 and Smad3, and immunohistochemistry and immunofluorescence staining for detection of the protein expression of phosphorylated Smad3 (p-Smad3), CTGF and COLⅠ. The results showed that TGF-β1 induced the expression of CTGF, COLⅠ, p-Smad3 and Smad7 in a time-dependent manner. The mRNA expression of CTGF and COLⅠ was significantly increased 24 h after TGF-β1 stimulation (P<0.01 for all). The protein expression of p-Smad3 and Smad7 reached a peak 1 h after TGF-β1 stimulation, much higher than the baseline level (P<0.01 for all). Pretreatment with high concentration of TSNⅡA resulted in a decrease in the expression of p-Smad3, CTGF and COLⅠ (P<0.01). The protein expression of Smad7 was substantially upregulated after pretreatment with two concentrations of TSNⅡA as compared with that at 2h post TGF-β1 stimulation (P<0.05 for low concentration of TSNⅡA; P<0.01 for high concentration of TSNⅡA). It was concluded that TSNⅡA may exert an inhibitory effect on cardiac fibrosis by upregulating the expression of Smad7, suppressing the TGF-β1-induced phosphorylation of Smad3 and partially blocking the TGF-β1-Smads signaling pathway. This study examined the effect of tanshinoneⅡA (TSNⅡA) on the cardiac fibrosis induced by transforming growth factor β1 (TGF-β1) and the possible mechanisms. Cardiac fibroblasts were isolated from cardiac tissues of neonatal Sprague-Dawley (SD) rats by the trypsin digestion The cells were treated with 5 ng / mL TGF-β1 alone or pretreated with TSNⅡA at different concentrations (10-5 mol / L, 10-4 mol / L). Immunocytochemistry was used for cell identification, RT- PCR for detection of the mRNA expression of connective tissue growth factor (CTGF) and collagen type I (COLI), Western blotting for detection of the protein expression of Smad7 and Smad3, and immunohistochemistry and immunofluorescence staining for detection of the protein expression of phosphorylated Smad3 (p-Smad3), CTGF and COLI. The results showed that TGF-β1 induced the expression of CTGF, COⅠ, p-Smad3 and Smad7 in a time-dependent manner. The mRNA expression of CTGF and CO The protein expression of p-Smad3 and Smad7 reached a peak for 1 h after TGF-β1 stimulation, much higher than the baseline level (P <0.01 for (P <0.01 for all) all). Pretreatment with high concentration of TSNIIA resulted in a decrease in the expression of p-Smad3, CTGF and COLI (P <0.01). The protein expression of Smad7 was substantially upregulated after pretreatment with two concentrations of TSNIIA as compared with that at 2 h post TGF-β1 stimulation (P <0.05 for low concentration of TSNIIA; P <0.01 for high concentration of TSNIIA). It was concluded that TSNIIA may exert an inhibitory effect on cardiac fibrosis by upregulating the expression of Smad7, suppressing the TGF- β1-induced phosphorylation of Smad3 and partially blocking the TGF-β1-Smads signaling pathway.