Abstract Purpose: We examined the effect of rapamycin on autoimmune myocarditis induced by cardiac myosin. Method: Cardiac myosin was injected to Lewis rats. Rapamycin was daily administered to the animals for 18 days. The rats were sacrificed after echo-cardiographic examination. Phosphorylation of Akt, ribosomal S6 protein 1(S6K1) or S6 protein was analyzed by Western blotting. Result: Phosphorylation of S6K1 or S6 was increased on 14 days after the immunization, and rapamycin completely suppressed the phosphorylation. Rapamycin improved the survival of the rats with autoimmune myocarditis. Rapamycin preserved cardiac function. Rapamycin attenuated the increase in BNP. Rapamycin suppressed the increase in the heart weight/tibial length ratio, and decreased the cellular infiltration and fibrosis of the myocardium. Conclusion: Rapamycin significantly attenuated ventricular remodeling induced by autoimmune myocarditis in rats.