A 78-year-old woman who had undergone an axillobifemoral artery bypass with a prosthetic graft for Leriche syndrome presented 1 month later with cough and fever. A clinical examination revealed obvious redness in the right groin. Routine laboratory tests uncovered inflammation and methicillin-sensitive-Staphylococcus aureus was cultured from blood samples. Mitral valve vegetations were identified by echocardiography, and after a diagnosis of infective endocarditis, specific intravenous antibiotics were immediately administered. One month later, CT revealed a large pseudoaneurysm of the posterior left ventricular wall that had not been present at the time of admission. Transesophageal echocardiography and magnetic resonance imaging showed an aneurysmal cavity arising from the wall just below the posterior mitral valve leaflet. The patient agreed to undergo cardiac surgery due to the high likelihood that the pseudoaneurysm would rupture. The mitral annulus and leaflet were normal at surgery. We resected the posterior leaflet, closed the cavity using a Xenomedica patch, and reconstructed the leaflet. We did not remove the pseudoaneurysm using an extracardiac approach because the likelihood of damaging the coronary arteries and the coronary sinus was quite high. The postoperative course was uneventful. At follow-up 1 year later, the patient was afebrile and both CT and echocardiography showed that the cavity was completely filled by the thrombus. The imaging findings were useful in determining the surgical approach.