Abstract: AIM:To study the changes of nitric oxide (NO) in mice with experimental autoimmune myocarditis (EAM). METHODS: A mouse model of EAM was established to observe the results at 21 days after immunization. RESULTS: Flow cytometric analysis showed that the ratio of splenic CD11b+F4/80+ macrophages was significantly increased in EAM mice. At the same time fluorescence probe detection demonstrated that the NO concentration in single macrophage cell was decreased. No obvious difference in NO concentration in the serum was observed between EAM mice compared to the control mice, but NO concentration in the heart of EAM mice was significantly increased compared with that in the control mice. Western blot analysis showed that endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) were both increased in the heart of EAM mice. CONCLUSION: NO may be a modulatory medium in the developmental process of autoimmune myocarditis.