We report the case of a man admitted for massive pulmonary embolism. Transthoracic echocardiography showed a serpentine thrombus in the right atrium across the foramen oval. Because of an acute worsening of the circulatory insufficiency, an intravenous thrombolysis was prescribed and the patient recovered progressively. An early control echocardiography showed the disappearing of the intracardiac thrombus and no evidence of abnormality of interatrial septum. While there was no evidence of venous thrombosis in legs, a renal cancer was diagnosed by echography. Silent stroke were highlighted at the scanner. This clinical case leads to discuss the origin of thrombus (in situ formation or thrombus migration) as well as the treatment (heparinotherapy, thrombolysis, surgical embolectomy, definitive closure of the foramen oval).