Eosinophilic myocarditis, light micrograph. Eosinophilic myocarditis is characterised by infiltration of endocardium and myocardium by eosinophilic infiltrate. There may also be peripheral blood eosinophilia. It is associated with drug/hypersensitivity reactions, infections (usually parasitic), hematologic malignancies (cancer) or may be idiopathic (of unknown cause).