Objective To investigate the effect of myeloid differentiation factor88 (MyD88)on the experimental autoimmune myocarditis (EAM) in Balb/c mice.MethodsTotally 90 Balb/c mice were randomly divided into three groups:MyD88 ( n =30),myocarditis ( n =30),and control ( n =30 )groups.An injection of MyD88 high expression adenovirus was carried out through vena caudalis at day 3.The mice of myocarditis group received porcine cardiac myosin at the same time and position.The mice of control group received PBS only.Serum and myocardium samples were gained at day 21.The inflammatory infiltration and the serum levels of cTnI,IgG,and IgM were examined.Results 21 days later,the inflammatory infiltration score of the myocarditis group was higher than the control group (2.39 ± 1.23 vs 0.68 ±0.65,P ＜0.05).The MyD88 group was significantly higher than the other 2 groups ( F =94.194,P ＜0.01 ),the myocarditis group ( 3.56 ± 1.34 vs 2.39 ± 1.23,P ＜ 0.05 ),and the control group ( 3.56 ±1.34 vs 0.68 ±0.65,P ＜0.01).The serum levels of cTnI,IgG,and IgM of the MyD88 group were significantly higher than the myocarditis group and the control group( P ＜0.01,P ＜0.05).Conclusions MyD88 participates in the pathogenesis of experimental autoimmune myocarditis in mice.