Moderate to severe pulmonary hypertension is considered to be an absolute contraindication to the performance of bidirectional Glenn (BDG) shunting. However, BDG shunting has been performed in young children with pulmonary hypertension associated with unrestricted pulmonary blood flow. In this study, the medical records of patients who underwent BDG starting from October 2000 to March 2004 were reviewed. Patients were divided into 2 groups on the basis of indexed pulmonary vascular resistance (PVRI) measured in room air: a high-risk group (n = 12) with PVRI > or = 3.5 Woods units (WU)/m(2) and a low-risk group (n = 28) with PVRI <3.5 WU/m(2) in room air. The 2 groups were comparable with respect to age, weight, ventricular morphology, pulmonary arterial anatomy, and atrioventricular valve function. Mean pulmonary arterial pressure and PVRI were significantly higher in the high-risk group compared with the low-risk group (39.2 +/- 20.7 vs 15.1 +/- 6.25 mm Hg, p <0.002, and 6.0 +/- 2.5 vs 1.6 +/- 0.82 WU/m(2), p <0.0005, respectively). The ratio of pulmonary flow to systemic flow was 1.45 +/- 0.76 in the high-risk group and 1.24 +/- 1.2 in the low-risk group. In the high-risk group, mean PVRI decreased to 2.0 +/- 1.0 WU/m(2) on 100% oxygen (p <0.0005). A contraindication to Glenn shunting was PVRI >3.5 WU/m(2) on 100% oxygen. Hospital mortality was 17% (2 of 12) in the high-risk group and 4% (1 of 28) in the low-risk group. Of 10 survivors in the high-risk group, 1 had undergone a Kawashima procedure, 7 had undergone Fontan procedures (with 1 death), and 2 were awaiting the completion of Fontan procedures as of this writing. In conclusion, these preliminary data suggest that in young children with increased pulmonary flow, BDG shunting can be safely performed, despite the apparent elevation of pulmonary arterial pressure to inoperable levels, provided PVRI decreases to < or = 3.5 WU/m(2) on 100% oxygen.