Initial dose effect of 5-fluorouracil: rapidly improving severe, acute toxic myopericarditis

5-Fluorouracil (5-FU) has a significant antineoplastic activity and has been used for the management of various malignant neoplasms. Cardiotoxicity of 5-FU is rare but may be life-threatening. A 55-year-old female patient was admitted to our hospital with atypical chest pain. Her electrocardiogram revealed widespread ST-segment elevations, and she had an elevated troponin level. Transthoracic echocardiography revealed global myocardial hypokinesia with impaired left ventricular systolic function (ejection fraction, 20%). Coronary angiography revealed normal coronary arteries with no vasospasm, and therefore, she was hospitalized with the diagnosis of acute toxic myopericarditis and was treated medically. In literature, this case is the first case of acute toxic myocarditis occurring because of the first dose of 5-FU.