Primary malignant fibrous histocytoma (MFH) of the heart is extremely rare. Herein, we report the case of a 17-year-old woman with a primary MFH in the right ventricular outflow tract, presenting with increasing dyspnea on exertion. Wide excision of the tumor, including part of the pulmonary artery and pulmonary valve, was performed under cardiopulmonary bypass. Her postoperative recovery was uneventful.