Eosinophilic myocarditis (EM) is a rare form of myocarditis that usually presents with heart failure due to eosinophilic infiltration. EM is often a component of hypereosinophilic syndrome (HES). HES is a rare disorder characterized by persistent, marked eosinophilia combined with organ system dysfunction. A 38-year-old man was admitted to emergency services with left inguinal pain and fever, and was hospitalized with diagnosis of nephrolithiasis and urinary tract infection. Intravenous antibiotic therapy of 3 grams meropenem per day and analgesic of 50 mg pethidine per day were administered. Typical angina pectoris and dyspnea developed approximately 24 hours after treatment. Rash on the chest, and diminished bilateral lung sounds and rales were observed. Nonspecific changes were present on electrocardiogram. Laboratory analysis showed progressively increasing levels of cardiac biomarkers and eosinophilia. Peripheral blood smear, bone marrow aspiration, and biopsy demonstrated eosinophilia. Chest x-ray revealed diffuse, bilateral interstitial and reticulonodular infiltrates. Transthoracic echocardiography showed thickened left ventricle. Coronary angiography revealed normal coronary arteries. EM was suspected, endomyocardial biopsy was performed, and pathologic specimen confirmed the diagnosis. Corticosteroid treatment was initiated, and within 1 day, angina pectoris and dyspnea had dramatically reduced, and cardiac biomarkers and eosinophil count had decreased. Normal chest x-ray was observed after 72 hours. The patient was discharged with steroid treatment.