A left ventricular aneurysm (LVA) is most commonly the result of myocardial infarction, usually involving the anterior wall. A left ventricular pseudoaneurysm (LVPSA) or false aneurysm forms when cardiac rupture is contained by adherent pericardium or scar tissue. The accurate diagnosis, although difficult to establish, is an important one to make because these aneurysms are prone to rupture. In this article, we report a challenging case of a cardiac aneurysm a year after a coronary bypass operation which could not be definitively diagnosed despite of imaging with different techniques including echocardiography, coronary angiography, left ventriculography and magnetic resonance imaging (MRI). The patient underwent a second cardiac surgery, the aneurysm was resected, the mitral valve was replaced and the defect in the ventricular wall was repaired. Because of the combined diagnostic capabilities like detailed and functional pathoanatomy and aneurysmal wall characterization, MRI seems to have multiple advantages in differential diagnosis.