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Background: Cardiac fibrosis is a common pathological progress of cardiovascular disease resulting from the excessive accumulation of extracellular matrix (ECM). Transforming growth factor (TGF)-β/SMADs pathway is a canonical signaling pathway which directly induces expressions of ECM related genes. Qishen Granule (QSG), a traditional Chinese formula developed from Zhen-Wu Decoration for heart failure (HF), has been proven to have definite therapeutic effects on cardiac fibrosis. However, its underlying mechanisms remain unclear.Purpose: To investigate the effects of QSG on TGF-β pathway and the downstream mediators including Smad3 and Glycogen synthase kinase (GSK)-3β.Methods: HF model was induced by ligation of left coronary artery on male Sprague-Dawley (SD) rats. Rat were randomly divided into four groups including sham group, model group, QSG group and Fosinopril control group. Rats in each group were treated for 28 days, and 2D echocardiography was adopted to evaluate the heart function. The degree of cardiac fibrosis was assessed by Hematoxylin-Eosin (HE), Masson's trichrome and Picrosirius red (PSR) staining. Contents of collagen Ⅰ and Ⅲ were assessed by immunohistochemical method. Expressions of genes and proteins in TGF-β/SMADs and PI3K-GSK-3 signaling pathways were detected by Real-time Fluorescence Quantitative PCR (RT-qPCR) and Western blot respectively. TGF-β1-treated cardiac fibroblasts of neonatal SD rats were adopted for in vitro studies.Results: 28 days after the surgery, cardiac ejection fraction (EF) and fractional shortening (FS) values in the model group showed a remarkable decrease, indicating the induction of HF model. QSG and Fosinopril elevated the EF and FS values, demonstrating cardio-protective effects. Pathological staining and immunohistochemistry showed that the contents of collagen I and III dramatically increased in the cardiac tissue of the model group compared with the sham group while QSG treatment reduced collagen contents. Furthermore, expressions of TGF-β1, p-Smad3 and p-GSK-3β were significantly decreased in the QSG treatment group compared with the model group, suggesting that the QSG may attenuate cardiac fibrosis through regulating TGF-β/Smad3 pathway. In vitro study further showed that the productions of type Ⅰ and Ⅲ collagen and α-smooth muscle actin (α-SMA) of cardiac fibroblasts were significantly increased by incubation with TGF-β1. QSG could markedly reduce the secretion of collagen Ⅰ and Ⅲ and α-SMA expression. Protein expressions of p-Smad3, PI3K, p-Akt and p-GSK-3β were significantly up-regulated by stimulation of TGF-β1. Treatment with QSG could suppress the activity of Smad3 and PI3K-GSK-3β signaling pathway in cardiac fibroblasts.Conclusion: QSG improves cardiac function through inhibiting cardiac fibrosis. The anti-fibrotic effects are potentially mediated by the inhibition of the TGF-β/Smad3 pathway and the phosphorylation of GSK-3β. [ABSTRACT FROM AUTHOR]