Idiopathic hypereosinophilic syndrome is a state of marked eosinophilia of unknown cause accompanied by multiple organ involvement. Any organ may be involved including bone marrow, heart, lung, gastrointestinal tract, liver, kidney and the nervous system. The common cardiac manifestations of hypereosinophlic syndrome are myocarditis, endocardial fibrosis, formation of mural thrombi, valvular hearat disease, restrictive cardiomyopathy and congestive heart failure. We report a case of a 61-year-old man with idiopathic hypereosinophilic syndrome manifested by myocarditis and severe pericardial effusion on transthoracicechocardiography that was successfully treated by pericardiocentesis and on-going steroid therapy.