Cardiac mass can be described as an abnormal structure within or directly contiguous to the heart. Tumors and thrombi are the most common types of cardiac masses. Intracardiac thrombi have been encountered in various clinical settings and can result in severe morbidity and mortality due to embolic events. Cardiac neoplasms are extremely rare, and are usually metastatic tumors. The major primary malignancies associated with cardiac metastases include cancers of the lung, breast, stomach, and liver, and lymphoma, leukemia, and melanoma. Osteosarcoma (OS) is the most common type of bone malignancy, and is almost always highly malignant. A previous study demonstrated that OS very rarely metastasizes to the heart. Presently reported is an unusual case of OS with intracaval, right atrial, and right ventricular extension that was misdiagnosed as venous thrombus.