We performed a retrospective echocardiographic study in tetralogy of Fallot (TOF) or pulmonay atresia with ventricular septal defect (PA&VSD) to evaluate the effects of Blalock-Taussig shunt on branch pulmonary artery growth. There were 35 patients with TOF and 11 with PA&VSD. We measured the right and left pulmonary artery area index and also the combined pulmonary artery area index, both before and after shunt operation. The mean +/- SD of these three variables before the shunt operation in the TOF group were 63.5 +/- 22.5, 57.8 +/- 24.9, and 121.4 +/- 42.8 mm(2)/m(2); after shunt operation they were 98.5 +/- 33.6, 85.9 +/- 31.9, and 184.0 +/- 59.8 mm(2)/m(2), respectively (p values <0.0001, <0.0002, and <0.0001, respectively). In the PA&VSD group the comparable values before shunt operation were 66.5 +/- 16.0, 55.4 +/- 10.6, and 120.9 +/- 26.9 mm(2)/m(2) and after shunt operation were 90.5 +/- 22.9, 77.2 +/- 24.1, and 166.6 +/- 44.4 mm(2)/m(2), respectively (p values <0.0006, <0.014, and <0. 002, respectively). We also examined the effect of distensibility of pulmonary arteries by comparing the percentage change in size of the combined pulmonary artery area index in the first 4 months after shunt with those after this time (p < 0.023). There were no significant differences between left- and right-sided shunts, origin and distal pulmonary artery growth, and the TOF and PA&VSD groups.