Objective:To evaluate the effects of Huoxin Pill (活心丸,HXP) on cardiac fibrosis and heart failure (HF) in isoproterenol (ISO)-induced HF rats.Methods:Thirty Wistar rats were randomly divided into 5 groups including control,HF,isosorbide mononitrate (ISMN),HXP low (HXP-L),and HXP high (HXP-H)groups (n=6 for each group) according to the complete randomization method.Rats were pretreated with ISMN(5 mg/kg daily),low concentration of HXP (10 mg/kg daily) or high concentration of HXP (30 mg/kg daily) or equal volume of saline by intragastric administration for 1 week,followed by intraperitoneal injection of ISO(10 mg/kg,14 days),and continually intragastric administrated with above medicines or saline for additional 6 weeks.The effects of HXP treatment on the cardiac function,heart weight index (HWI),pathological changes,and collagen content were further assessed.Moreover,the role of HXP on activation of transforming growth factor-β 1 (TGF-β 1)/Smads pathway was further explored using immunohistochemistry (IHC) and Western-blot assay.Results:HXP treatment significantly alleviated the decrease of ejection fraction (EF) and fractional shortening (FS),while decreased the elevation of left ventricular end-systolic volume (LVESV) in ISO-induced HF rats (P＜0.05).Moreover,HXP treatment obviously attenuated the increase of HWI and serum level of creatine kinase MB (CK-MB,P＜0.05),as well as pathological changes in ISO-induced HF rats.Further determination indicated that HXP treatment alleviated the elevation of collagen Ⅰ and collagen Ⅲ protein expression in cardiac tissues of ISO-induced HF rats.Furthermore,HXP treatment significantly down-regulated the increase of TGF-β 1 and p-Smad2/3 protein expression in cardiac tissues of HF rats (P＜0.05),while did not affect the expression of total Smad2/3.Conclusions:HXP attenuated heart failure and cardiac fibrosis in ISO-induced HF rats by suppression of TGF-β 1/Smad2/3 pathway.