Balloon dilation of the pulmonary valve was performed in 54 patients with tetralogy of Fallot with severe cyanosis, high haematocrit and severe valvar pulmonary stenosis. Clinical, echocardiographic, angiographic, and haemodynamic data were analyzed before and after the procedure. After balloon dilation, the systemic oxygen saturation increased from a mean value of 66% to 85%. The mean value of the haematocrit before dilation was 55 + 13, and decreased to 47 after dilation (p < 0.002) in 2 months follow-up. Balloon dilation increased the size of the pulmonary valvar orifice from a mean value of 9 + 5 mm to 11.5 + 2 mm (p < 0.005). The mean Z score of the pulmonary valves, which was -3 + 1.3 before dilation, increased to -1.1 + 1.1 immediately after the procedure (p < 0.05). The size of the right and left pulmonary arteries increased after dilation from 9 mm to 10 mm, and from 8.7 + 2.4 mm to 9.8 + 2.3 mm, respectively (p < 0.05). The comparable mean Z scores increased from -2.8 + 1.9 SD to -1.8 + 1.4 SD, and from -2.4 + 1.9 SD to -1.5 + 1.6 SD for the right and left branches, respectively (p < 0.05). In patients with stenosis at the bifurcation of the pulmonary trunk and hypoplasia of the left artery, successful dilation of the pulmonary valve lead to an increase of flow and improvement in size of the hypoplastic segment. In conclusion, initial balloon dilation of the pulmonary valve in tetralogy of Fallot resulted in increase of the Z score for the pulmonary valve and improved antegrade pulmonary blood flow, inducing growth of the pulmonary arteries and ameliorating the anatomic and physiologic preoperative condition.