Postinfarction ventricular aneurysms may be either true or false, each with apparently definite diagnostic criteria on imaging techniques. We present the case of a 69 year-old male admitted to our hospital 6 weeks after an acute anterior myocardial infarction, for progressive exertional dyspnea. Transthoracic echocardiography demonstrated a large cystic cavity, 10 cm in diameter, communicating with the left ventricle's apex through an orifice of 5 cm diastolic diameter. The echocardiographic diagnosis was of a large, saccular aneurysm. Contrast ventriculography confirmed the existence of a large cavity connected to the apex of the left ventricle, 12 cm in diameter, with sluggish flow of contrast within it and features suggestive of pseudoaneurysm. The patient was referred for surgery because of continued symptoms and a preoperative diagnosis of either a large ventricular aneurysm or pseudoaneurysm. At the time of surgery a true aneurysm was found. We present this case because the rarity of a saccular configuration of a postinfarction left ventricular aneurysm, because of the unusual large size of it and to point on the possible disagreement between the conclusions of imaging modalities in differentiating a true from a false aneurysm.