The authors report the case of a 69 year old man with a large left ventricular thrombosis complicating anterior myocardial infarction occurring three years previously for which anticoagulant therapy had to be withdrawn. The discussion is based around the large size of the thrombus, its complete regression with anticoagulant therapy (heparin and coumarin-derivative) and also around the detection of spontaneous echo contrast in the left ventricle by transoesophageal echocardiography. This case underlines the probable risk of withdrawing anticoagulant therapy in patients with severe left ventricular dysfunction and left ventricular spontaneous contrast.