A 25-year-old female presented with high fever and dyspnea. She was diagnosed as infective endocarditis, severe mitral regurgitation, grade II A-V block and acute left heart failure We performed emergency mitral valve replacement. At operation, mitral ring abscess was found which was extended to submitral left ventricular wall. The abscess was excised and the defect of mitral annulus was repaired with Xenomedica patch. Left ventriography at 30 days after the operation showed a submitral left ventricular pseudoaneurysm (size: 30 x 26 x 33 mm) without evidence of infection. Further examinations showed that the aneurysm extended to the annulus of tricuspid valve through interatrial septum. About 1 year after the operation, she had paroxysmal atrial fibrillation due to right atrial overloading. We decided to perform reoperation. At reoperation, the ostium of the aneurysm was closed with a Xenomedica patch after taking off the prosthetic valve. It was very difficult to close the ostium because we could not see the submitral ventricular wall directly. Although postoperative course was good, she had complete A-V block necessitating permanent pacemaker.