Glucose-insulin-potassium (GIK) is a useful adjunct to myocarditis. Besides its essential action in energy metabolism, insulin also exerts an anti-inflammatory effect. This study investigated the effect of insulin on myocardial inflammation in experimental autoimmune myocarditis (EAM) in mice and its potential role in T cell regulation. Mice were divided randomly into a normal control group, a saline-treated EAM group and an insulin-treated EAM group. The histopathological changes of myocardium, α-myosin heavy chain (MyHCα)614–629 antigen-specific autoantibody titre, the serum level of cardiac troponin I (cTnI), mitogen-activated protein kinase (MAPK) family members' activity and content were measured. Furthermore, the phenotype of T lymphocyte subsets in splenocytes was analysed to evaluate the immune status of mice. Insulin reduced serum cTnI of EAM mice on days 14 and 21 (P < 0·05) after immunization, with no changes in blood glucose and autoantibody production. Western blot revealed that extracellular signal-regulated protein kinase (ERK1/2) may be a determining factor in this process. Total ERK1/2 and phospho-ERK1/2 (p-ERK1/2) were both up-regulated in insulin-treated mice after immunization. We also found that insulin treatment promoted T cell recovery without changing the naive-to-memory T-cell ratio; in particular, CD3+ T cells in insulin-treated mice proliferated more vigorously than in control mice (P < 0·05). We report here for the first time that insulin alleviates myocarditis in the EAM model. These data show that insulin has a direct effect on T cell proliferation in EAM. It is possible that GIK or insulin may assist T cell recovery towards normal in myocarditis, especially for diabetic or hyperglycaemic patients.