The authors describe a case of a patient with congestive heart failure complicated by syncope, hypotension and a transitory state of vigil coma. The transthoracic and transesophageal echocardiogram showed a huge mass that occupied almost totally the right ventricle causing sever obstruction. The patient was submitted to surgery and a resection of the mass with reconstruction of the free right ventricle wall was done. The histopathology revealed to be a leiomyosarcoma. There was a previous history of an uterine surgery.