Primary cardiac extrasceletal osteosarcomas are uncommon tumours. They have aggressive behaviour and thus poor prognosis. This report describes a 40-year old female patient who was referred to our hospital with dyspnoea, weakness and syncopal attacks. Echocardiography and chest computed tomography showed a left atrial mass, and tumour excision revealed a cardiac chondroblastic osteosarcoma. After pathological diagnosis, she was scheduled for chemotherapy and radiotherapy by the related departments.