A false aneurysm of the left ventricle was successfully operated upon in a patient who had developed postoperative purulent pericarditis after resection of a post-infarction ventricular aneurysm 5 months previously. The authors describe the clinical, anatomical, radiological, and ultrasonographic characteristics of false aneurysms, which occur more frequently after myocardial infarction than postoperatively. Other, more rare causes are described, as well as recent data reported in published literature. The role of infection in certain postoperative forms is emphasized. Apart from angiography, non-invasive methods such as bidimensional ultrasonography and angioscintigraphy play an important role in establishing the diagnosis, avoiding explorations which are not without risk in debilitated patients. The frequency with which rupture of false aneurysms is observed, in contrast with true aneurysms, entails early recognition and operation on a regular basis, even when signs of intolerance are absent.