A 54-year-old female presented with shortness of breath and cyanosis. Work up with chest X-ray and subsequent echocardiogram revealed an intracardiac bi-atrial mass leading to emergent cardiothoracic resection. Pathology was consistent with a primary cardiac high-grade osteosarcoma. Post-resection staging positron emission tomography-computed tomography (PET-CT) showed hypermetabolic mixed lytic and sclerotic lesion of T10 concerning for metastasis. She received five cycles of adriamycin and ifosfamide chemotherapy before discontinuation due to systolic dysfunction. Nine months later, she developed a high tumor burden with progressive disease and was treated with second-line gemcitabine/docetaxel with disappointing results. She is currently on treatment with cyclophosphamide and topotecan as third-line treatment with an excellent clinico-radiographic response. Osteosarcomas are aggressive with a high incidence of recurrence and metastasis. Fewer than 50 cases of primary cardiac osteosarcomas have been reported in the literature. Even though complete resection can be achieved in some cases, long-term results are usually poor. No standard therapy has been established.