Balloon angioplasty of stenosed Blalock-Taussig anastomosis: role of balloon-on-a-wire in dilating occluded shunts. Six children with cyanotic congenital heart defects, aged 6 to 60 months, underwent percutaneous balloon angioplasty of a narrowed Blalock-Taussig (BT) shunt to improve arterial oxygen saturation. The indication for angioplasty was a cyanotic heart defect not amenable to total surgical correction, either because of the age and size at presentation or because of anatomic complexity, but at the same time requiring palliation of pulmonary oligemia. Following balloon angioplasty, there was an increase in arterial oxygen saturation from 71 +/- 8% to 81 +/- 6% (p less than 0.05). In one child with long segment narrowing, there was no significant improvement in oxygen saturation, and this child underwent an additional BT shunt on the contralateral side. On follow-up 3 to 12 months after balloon angioplasty, the oxygen saturations remained improved (78 +/- 10%) in the remaining five patients. In two children with either complete or almost complete blockage of the BT shunt, we were unable to advance any catheter across the shunt but we were able to advance a 2 or 3 mm balloon on a wire and dilate the shunt, followed by introduction of a catheter carrying a larger balloon for angioplasty. This has permitted us to obtain the pulmonary artery pressure directly (this information was of obvious value in patient management) and resulted in an improvement in the arterial oxygen saturation. It is concluded that (1) balloon angioplasty of narrowed BT shunts is feasible, effective, and safe and (2) even completely occluded shunts can be cannulated and the balloon dilated with the newly available balloon-on-wire devices. 