A 66-year-old woman had suffered from repeated heart failure beginning 6 years after mitral valve replacement. Left ventricular pseudoaneurysm was discovered 9 years after the replacement, while no evidence including histology was obtained for the cause of the pseudoaneurysm except the mitral valve replacement. The progression of aortic valve stenosis and the formation of the pseudoaneurysm may have contributed to the onset of congestive heart failure. Surgical treatment was successful. Although left ventricular pseudoaneurysm after mitral valve replacement is rare, careful echocardiographic examination is necessary for detecting such a complication in patients after surgery.