A 77‐year‐old woman underwent mitral valve replacement and tricuspid annuloplasty for severe mitral stenosis and tricuspid regurgitation with pulmonary hypertension. Two months later, the patient was readmitted because of marked edema. A new harsh pansystolic murmur was auscultated, and echocardiography revealed a jet from the left ventricle to the right atrium but no paravalvular leakage was detected at the mitral valve position. At operation, an 6 mm defect adjacent to the tricuspid annulus in the interatrial septum and detachment of the anterior edge of the tricuspid ring were detected. The defect was closed using a pericardial patch. An inadequate stitch at the anteroseptal commissure in the previous operation led to left ventricular‐right atrial communication.