The case reported in this paper, besides illustrating several aspects of the eosinophilic myocarditis, documents a yet undescribed feature of the cardiac involvement in idiopathic hypereosinophilic syndrome characterized by marked basement membrane thickening of small intramyocardial vessels. We are unaware of previous reports showing the presence of an extensive thickening of the basement membrane of arteriolar and capillary intramyocardial vessels in eosinophilic myocarditis. Considering the findings in the present case, i.e., the focal nature of the lesions, the type of necrosis, and the diffuse microangiopathy, it can be hypothesized that the microvascular disease could play a role in the development of the myocardial changes.