The idiopathic hypereosinophilic syndrome (HES) is a leukoproliferative disorder characterized by sustained eosinophilia (> 1.5 × 10<sup>9</sup>/l) and (multi-)organ dysfunction caused by infiltration of eosinophils. Especially the heart is frequently affected. In this report, we describe 2 patients with HES and Löffler’s endomyocarditis. Prednisone is the drug of choice for treatment. Both our patients responded very well to prednisone and came into remission. If prednisone fails, there are other therapeutic options like myelosuppressive drugs (hydroxyurea and vincristine) or interferon-α. We review the literature with regard to clinical presentation, diagnosis and treatment.