A patient underwent mitral valve replacement in 1966 for severe mitral valve disease. The initial clinical result was excellent but symptoms recurred nine years later, and since 1969 he has had progressive cardiac enlargement. At present he is in functional class II and has massive cardiomegaly with gross enlargement of the left atrium, right ventricle, and right atrium. Cardiac catherisation showed "normal" prosthetic valve function, but on moderate exercise he developed severe left atrial and pulmonary arterial hypertension. His clinical course illustrates a long-term sequela of "valve prosthesis--patient mismatch".