Complete relief of the outflow tract obstruction of the right ventricle is essential for successful surgical correction of the tetralogy of Fallot. Pulmonary valvulotomy and/or infundibulectomy will be adequate in many cases. In others, however, a significant narrowing will remain. This is usually a consequence of a small pulmonary valve annulus and some hypoplasia of the proximal main pulmonary artery, but it may be due to a small infundibular region (even after extensive resection of infundibular muscle), or in some instances to a combination of these abnormalities. A "roof" must be used in these cases to widen further the right ventricular outflow tract. Various materials have been used to construct a patch for this area. This report concerns the long-term evaluation of free grafts of autogenous right atrium used for this purpose. Materials and Methods Mongrel dogs were anesthetized, and moderate hypothermia was induced by immersion. Bilateral thoracotomy was performed;