The patient was a 29-year-old woman who, when she was an 8-year-old, had undergone atrial septal defect (ASD) closure and mitral valve replacement (MVR) using a Björk-Shiley valve (25 mm) for Lutembacher syndrome. Because of a planned pregnancy, warfarin had been replaced by heparin. During the 7th week of pregnancy, she was admitted to our hospital because of dyspnea. She was diagnosed with acute heart failure due to prosthetic valve thrombosis. Following termination of pregnancy, the mitral valve was replaced with an ATS valve (25 mm). She was discharged 10 days after surgery without complications.