To explore the impact of hydrogen sulfide (H2S) on the heme oxygenase—1 (HO—1)/carbon monoxide (CO) system in coxsackie virus B3 (CVB3)—induced myocarditis. A total of 80 Balb/c mice were divided randomly into four groups designated N, C, P and S. Group N served as the negative control while groups C, P, and S were infected with CVB3 to induce myocarditis. Group P was additionally treated with DL—propargylglycine (PAG) to inhibit the generation of H2S while Group S was treated with NaHS, an H2S donor. Ten days after infection, heart sections were scored for histopathology. We also measured carboxyhemoglobin (COHb) levels in the blood and HO—1 expression by immunohistochemistry. 1. Each CVB3—infected group (C, P, and S) exhibited increased pathology, COHb levels, and HO—1 expression compared to uninfected controls. 2. Regarding histopathology, the score of group P was worse, while that of group S was better, than that of group C. 3. The P group COHb level was lower than group C, while the S group COHb level was higher than group C. 4. Positive HO—1 expression was seen in group C with reduced expression in group P and increased expression in group S. 5. A positive correlation was observed between the COHb concentration and HO—1expression; alternatively, a negative correlation was found between the histopathologic scores and both the concentration of COHb and the expression level of HO—1. Modulation of H2S can play a regulatory role in the pathogenesis of VMC by impacting the HO—1/CO pathway.