Cardiac metastases are between 40 and 100 times more frequent than primary tumors and generally occur at a very advanced stage of the cancerous disease. Cardiac metastases are frequently found in lung, breast, kidney and melanoma cancers [1]. Cardiac metastases are often asymptomatic, and incidentally discovered during a cardiac assessment, as is the case of our patient, or during autopsies [2]. The frequency of cardiac metastases from thyroid cancers is very low, between 0% and 2%, in two large series of autopsies [3,4]. Anaplastic thyroid cancer (ACT) is considered one of the most aggressive neoplasms encountered in humans [5]. Echocardiography allows the diagnosis of cardiac metastases in the form of rounded, sessile pericardial masses or, on the contrary, oblong. If the MRI does not confirm the malignancy of a tumor, certain criteria are very suspicious: A poorly circumscribed nodular mass, a mobile intracavitary mass, polylobed with a hypersignal in T1, an extracardiac tumor syndrome compressing the heart cavities, invasion of the inferior vena cava. Gadolinium injection allows better visualization of the tumor and its extension [6]. At the stage of cardiac metastases, the treatment is most often palliative [6], surgery can rarely be performed. And the prognosis in this case is very pejorative. For a localized form, treatment with chemotherapy or targeted therapy followed by radiotherapy is recommended as an adjuvant [7].