Primary cardiac osteosarcomas are uncommon tumors. They have an aggressive biology and hence poor prognosis. This report describes a 23-year-old male patient who was referred to our hospital with chest pain. Echocardiography showed a left atrial mass, and tumor excision revealed a cardiac osteosarcoma. Adjuvant cisplatin plus ifosfamide combination chemotherapy provided a disease-free survival of 9 months; unfortunately the patient died of metastatic disease thereafter.