Objective To study the expression of osteopontin (OPN) and collagen type Ⅰ in the rat myocardial fibroblasts infected by coxsackievirus B3 (CVB3) and to explore the possible pathogenesis of OPN on viral myocarditis.Methods Cardiac fibroblasts were isolated from neonatal rat and cultured with an traditional method.The primary cultured rat myocardial fibroblasts were infected by CVB3 which multiplicity of infection (MOI) was 0.5 PFU/cell.The myocardial fibroblasts were divided into control group 12 h and CVB3 groups (infected after 12 h,1 d,2 d,3 d).The expression of OPN and collagen type Ⅰ were detected by RT-PCR,Western Blotting and immunohistochemistry.And the linear correlation between the expression of OPN and the expression of collagen type Ⅰ was analyzed.Results ( 1 ) The gray scale values of the OPN/β-actin in control group(12 h)and viral groups (12 h,1 d,2 d,3 d) were 0.38 ± 0.06,0.56 ± 0.06,0.72 ± 0.05,0.98 ± 0.06,0.86 ± 0.02 respectively with RT-PCR,and were 0.26 ± 0.03,0.36 ± 0.03,0.52 ± 0.04,0.76 ± 0.05,0.62 ± 0.02 respectively with Western Blotting.The expression of OPN was found to be increased after 12 h infection,reached to the maximum after 2 d infection and displayed a decreased tendency after 3 d infection.There was significant difference on the gray scale values of the OPN/β3-actin ( F=74.965,53.004,respectively,P ＜ 0.05 ).(2) The gray scale values of the collagen type Ⅰ/β-actin in control group (12 h)and viral groups (12 h,1 d,2d,3 d) were 1.12 ± 0.03,1.18 ± 0.01,1.22 ± 0.02,1.33 ± 0.02,1.28 ± 0.03,respectively with RTPCR.These results suggested that the collagen type Ⅰ expression started to increase at 12 h when infected by CVB3,reached to the maximum at 2 d,and then decreased after 3 d infection,the difference was significant ( F =38.241,P ＜ 0.05).(3) The expression of OPN was positively correlated with the expression of collagen type Ⅰ ( r=0.948,P ＜ 0.001 ).Conclusion CVB3 can induce the expression of OPN and collagen type Ⅰ in the rat myocardial fibroblasts and the expression of OPN and collagen type Ⅰ displays positive correlation.It suggests that OPN can promote the expression of collagen type Ⅰ in myocardial fibroblasts,and may play an important role in the pathogenesis of viral myocarditis.