Balloon valvoplasty was undertaken in 27 patients with tetralogy of Fallot for first-stage palliation. Indications were arterial saturation of oxygen < 80%, hypoxic spells and duct-dependant pulmonary perfusion. The dilation was performed following diagnostic heart catheterization. Saturations improved from 75% +/- 8.5 before valvoplasty to 85% +/- 8.4 after the procedure, and worsened little to 83% +/- 9.6 at follow-up after 3.4 months. The pulmonary valvar orifice was hypoplastic in most patients (Z = -3.3 +/- 1.2), and did not change after the procedure. The cross-sectional area of the pulmonary arteries was diminished initially, reflected by a Nakata index of 186 +/- 95 mm2/m2. After valvoplasty, we found widening of the vessels (Nakata index 225 +/- 100 mm2/m2). At follow-up no further growth of the arteries was observed (Nakata index 209 +/- 109 mm2/m2). The procedure was complicated by hypoxic spells in three patients which were controlled by intravenous propranolol, and deep venous thrombosis in four patients. Our data demonstrate that balloon valvoplasty is feasible for initial palliation in patients with tetralogy of Fallot. It does not, however, produce growth of the pulmonary arteries or of the pulmonary valve.