The most common organ to which osteosarcomas metastasize is the lungs. Extrapulmonary osteosarcoma metastases are being observed in increasingly more patients, particularly after pulmonary metastases, and becoming less sensitive to chemotherapy with shorter survival. Surgical resection is advocated for prolonging survival and improving quality of life when the primary tumor is under control. In this article, we present a case of mediastinal osteosarcoma metastasis with left atrium invasion in a 25-year-old female patient. During her seven-year oncologic follow-up, patient was performed two right, two left thoracotomies for pulmonary metastasectomies and one right Dartevelle incision for metastasis located in the right upper lobe extending through the clavicle and the first rib. She was also performed a median sternotomy for resection of a mediastinal metastasis adjacent to both atria. Patient received radiotherapy and several courses of adjuvant chemotherapy throughout her therapy. On patient's final computed tomography scan, mediastinal tumor recurrence was detected which was invading the left atrium. Considering that surgical resection would be the most appropriate therapeutic approach to prolong survival, patient was performed metastasectomy under cardiopulmonary bypass support and cardiac arrest with partial left atrial resection and bovine pericardial patch. Keywords: Cardiopulmonary bypass; metastasectomy; osteosarcoma.