We report on a 6-year old boy with tetralogy of Fallot and pulmonary atresia in whom a 16 m Matrix P conduit was implanted between the pulmonary artery and the right ventricle at the age of 16 months. Five years later he developed severe stenosis of the distal conduit anastomosis. The notable findings were several aneurysms of the conduit proximal to the distal stenosis within the high-pressure region. The wall of the aneurysms contained xenogeneic conduit tissue without inflammatory or foreign-body response. We believe that aneurysm formation of the conduit was a result of fatigue of the conduit wall under suprasystemic pressure.