A 43-year-old man had an incidental finding of a large anterior mediastinal mass. He suddenly presented with unstable angina and an emergency coronary angiogram showed severe proximal circumflex artery and left anterior descending artery stenosis from external compression. He underwent emergency coronary artery bypass graft surgery and excision of the tumor. At surgery, the tumor was found to be invading the left ventricle, so debulking of the mediastinal tumor was performed. Histology showed a biphasic pericardial synovial sarcoma. The patient was recommended chemotherapy and radiotherapy but he refused. He died 13 months after surgery.