Balloon dilatation was successfully performed in two patients with complete obstruction of the superior vena cava baffle junction after a Mustard operation for transposition of the great arteries. Evidence for complete relief of obstruction in the first patient, aged 4 years, was obtained by angiography, which showed improved calibre at the site of obstruction and improved haemodynamic pressure measurement after the balloon dilatation. In the second patient, aged 14 years, the relief was incomplete; in this patient a 3 cm long 3 mm diameter Palmaz stent was successfully implanted.