Abstract： Objective To explore the effects of the β3 adrenergic receptor (β3-AR) agonist BRL37344 on cardiac fibroblast proliferation and collagen fiber hyperplasia in Wistar rats by promoting the phosphaticlylinositol 3 kinase-protein kinase B(PI3K-Akt) signal transduction pathway. Method Cardiac fibroblasts(CFbs) were isolated from 1 - 3 day-old Wistar rats under the sterile environment in the laboratory of the First Affiliated Hospital of Hasbin Medical University, by using enzyme digestion and an modified technique of differential anchoring velocity.The cultured myocardial cells were randomly (random number) divided into five groups. ① In blank group, rats were not treated with drug; ②in BRL group, rats were treated with BRL37344; ③in LY group, rats were treated with LY294002(PI3K antagonist) for one hour before treated with BRL37344;④in Akt-Ⅰ group,rats were treated with Akt-Ⅰ (Akt antagonist) for one hour before treated with BRL37344;⑤in L-A group, rats were treated with LY294002 and Akt-Ⅰ for one hour before treated with BRL37344. MTT colorimetric method and RT-PCR were used to observe the role of β3-AR agonist with or without PI3K antagonist and/or Akt antagonist in cardiac fibroblast proliferation (CFP) and collagen fiber hyperplasia (CFH). Comparisons between groups were made by one-way ANOVA and Tukey test. Results ①β3-AR was present in the CFbs. ②Compared with BRL group, the CFP and CFH in LY and Akt-Ⅰ groups were lower (P ＜0.01) and those in L-A group were lowest (P ＜ 0.01). ③Compared with blank group,the expressions of type Ⅰ and type Ⅲ fiber mRNA obliviously increased in BRL group (P ＜ 0.01),and at 48 hours,the expressionrs reached peak. At 48 hours,compared with BRL group,the expressions in LY and Akt-Ⅰ groups were lower, and were lowest in L-A group ( P ＜0.01). Conclusions BRL37344 promotes cardiac fibroblast proliferation and expressions of type Ⅰ and Ⅲ collagen fiber mRNA by activating the PI3K-Akt signal transduction pathway.