A case of a thrombosed Björk-Shiley mitral valve with severe pulmonary edema which developed six years following an initial operation was reported. Doppler echocardiography was one of the most useful tools to evaluate prosthetic mitral valve dysfunction. Peak blood flow velocity was high (2.7 m/sec) compared to the data (1.7 m/sec) obtained six months before the reoperation. Emergency surgery disclosed the thrombosed valve prosthesis which was replaced with a St. Jude Medical valve. The patient recovered successfully with no problems.