Diagnosis of so-called false aneurysms of the left ventricle after infarction is judged to be important because the risk of rupture is high and resection of aneurysms with a narrow orifice is usually successful. Aneurysms with larger communication orifices are less likely to rupture. Echocardiographic and angiographic criteria have been devised to classify left ventricular aneurysms into two distinct types. In four cases of inferior aneurysms the echocardiographic and angiographic criteria were typical of a "false aneurysm" but the defects were diagnosed as true aneurysms after intraoperative and histological examination. These aneurysms were characterised by their site in the inferior wall and by late diagnosis and treatment, which may have influenced their occurrence and determined the development of their characteristic shape. These findings suggest that the classic echocardiographic and angiographic diagnostic criteria for "false" aneurysms may have to be abandoned.