Background: Gualou Xiebai Decoction (GXD) is a well-known traditional Chinese recipe.It has been used to treat cardiovascular disorders for nearly two thousand years.But there is a lack of reports on cardiac fibrosis and underlying mechanism.Methods: Myocardial infarction was performed by ligation of left anterior descending coronary artery (LAD) in male Wistar rats.Rats with myocardial infarction were treated with GXD (1.14 g/kg, 4.53 g/kg) daily for 4 weeks.Cardiac function was evaluated by echocardiography.Hemodynamic parameters and infarct size were measured in each group.Myocardial enzymes were examined by biochemical tests.Inflammatory cytokines were assessed by ELISA, and interrelated proteins were detected by western blot.Results: Cardiac function was significantly improved in GXD-treatment rats after myocardial infarction (MI), which was accompanied with decreased infarct size.Administration of GXD to myocardial fibrosis rats significantly ameliorated the activities of AST, LDH and CK-MB in serum.The increase in inflammatory factors (TNF-α, IL-1β) were markedly reduced upon GXD treatment.Furthermore, the inflammatory mediators (NF-κB p65, TNF-α, MCP-1) were down-regulated by GXD in the myocardial fibrosis rats.Conclusions: Treatment with GXD improved cardiac function induced by myocardial fibrosis by inhibiting expression of inflammatory mediators associated with NF-κB.