Uterine leiomyosarcomas (ULMS) are rare malignant tumors of smooth muscle origin. Cardiac metastases from ULMS are extremely uncommon and remain underreported. Herein, we present the case of a 57-year-old woman with locally advanced uterine leiomyosarcoma who developed an intracardiac metastasis. Following chemotherapy, radiotherapy, and subsequent surgery for the primary tumor, postoperative imaging unexpectedly revealed a massive right atrial thrombus extending into the inferior vena cava, later confirmed to be metastatic. Despite surgical intervention, complete resection of the thrombus was not achieved, leading to the patient's demise from progressive heart failure. This case emphasizes the potential for cardiac involvement in ULMS and highlights the importance of considering metastatic cardiac lesions in the differential diagnosis of intracavitary masses.