Seventeen patients 1 day to 28 months old with congenital cyanotic heart disease underwent a modification of the Blalock-Taussig shunt. Eight were newborn infants weighing 2.6 to 4.8 kg. All infants had complex congenital heart defects that were not considered amenable to early correction. There were no early deaths and no shunt failures. Postoperative complications were restricted to prolonged intubation in 2 patients and a subcutaneous wound infection in a 14-day-old infant. Follow-up from 1 to 31 months revealed minimal cyanosis, stable hemoglobin levels, and good shunt murmurs, and there have been no upper extremity complications. There were 2 late deaths; 1 (the oldest patient) was related to medication, and the second resulted from small bowel necrosis. The concept of the azygos vein patch modified Blalock-Taussig shunt involves two factors: (1) mobilizing as much length as possible of the subclavian artery in spite of its distal small size to allow for a tension-free shunt to prevent tension on the anastomosis as growth occurs, and (2) enlarging the subclavian artery distal to the vertebral artery origin with an autologous azygos patch. During performance of a standard Blalock-Taussig shunt, a longitudinal incision is made through the pulmonary artery across the anastomosis into the upper subclavian artery. The appropriate length of harvested azygos vein is used as a patch angioplasty across the shunt. A tension-free shunt with a patulous distal portion is achieved. Pulmonary overcirculation is avoided by the limiting size of the proximal subclavian artery. Temporary occlusion of the shunt at operation resulted in an increased mean blood pressure from 6 to 18% in all infants.(ABSTRACT TRUNCATED AT 250 WORDS)