We comment on an article published by Mansouri in the . L-arginine (L-Arg), a dietary supplement, is a precursor of nitric oxide, can improve cardiovascular disease, and it is important for treating heart disease and hypertension. Previous studies have demonstrated a beneficial effect of L-Arg on diabetes. In the study by Mansouri , L-Arg moderately increased blood glucose levels in normal rats. However, in diabetic rats, L-Arg significantly increased lipid levels, which is different from the findings of previous studies. This study demonstrated that a safe dose of 0.5 g/kg in diabetic rats can improve the lipid profile and decrease body weight. However, high doses (1 g/kg or higher) may aggravate damage to myocardial tissue in diabetic rats by increasing blood glucose, inflammation, and oxidative stress. Therefore, this study further demonstrated that high doses of L-Arg can exacerbate myocardial injury in diabetic patients.