Cardiotoxicity by 5-fluorouracil has been reported as a rare complication in treatment protocols for adult patients with different malignant diseases. The combination with folinic acid as a biomodulatory substance and other cytotoxic drugs has been introduced to render protocols more effective and less toxic. We report severe but completely reversible cardiotoxicity of a treatment protocol for nasopharyngeal tumor (Schmincke tumor) of pediatric patients consisting of 5-fluorouracil, methotrexate, cisplatin and folinic acid in a 14-year-old boy who had no preexisting cardiac disease. The pathomechanism is briefly discussed.