Ebstein anomaly of the tricuspid valve is a well known malformation of the heart, but this occurrence in the mitral valve is a very rare congenital heart disease. In this case report a two years and nine months old girl with symptoms of heart failure during the first year of life due to severe mitral regurgitation was studied. The echocardiographic and angiographic features were typical of the Ebstein malformation of the mitral valve. The surgical treatment was made with implantation of pericardial bovine bioprothesis in the mitral position, without ressection of the natural valve tissue. The surgical features confirmed the diagnosis and the postoperative evolvement is excellent.