The prognosis of Tricuspid Atresia, a rare congenital heart disease, has been changed by surgery. The criteria for Fontan operation have been well established in the literature and adult patients rarely fulfil these criteria; however, in very selected cases Fontan operation can be performed also in adults. A 33 year old woman with tricuspid atresia and previous palliation with classical right Glenn and with left modified Blalock-Taussing, underwent modified Fontan operation because increasing cyanosis and moderate exercise intolerance. Three weeks after operation the patient was readmitted with severe heart failure because of a tight obstruction at the anastomosis between right atrium and main-left pulmonary artery. The stenosis was treated with balloon and stenting achieving large pathway. Our experience confirms that after a modified Fontan, if cardiac failure occurs, an immediate full investigation have to be done.