A 70-year-old female with a history of rheumatic heart disease underwent rereplacement of mitral valve mechanical prosthesis in May 2003. Seven months later, she presented with progressive exertional dyspnea, exercise intolerance, and a new holosystolic/diastolic murmur. Echocardiography confirmed a large shunt through a fistula in the inferior limbus of the atrial septum with left ventricular-to-right atrial communication. We report the novel use of the Amplatzer duct occluder for closure of the fistulous tract.