The bidirectional superior cavopulmonary anastomosis, commonly referred to as bidirectional Glenn shunt (BDG), is a commonly performed procedure for a variety of cyanotic congenital heart diseases that leads eventually to single-ventricle repair.It is an important intermediate palliation in patients with a structurally or functionally univentricular heart who are ultimately destined to have a Fontan-type operationAnd It is usually performed under cardiopulmonary bypass (CPB), with its associated complications and costs. Avoiding the use of CPB is associated with significant elevation of the proximal superior vena cava (SVC) pressure, which may lead to neurological insults. However, the safety of performing BDG without CPB has been reported by many authors and most of these reports have recommended some decompression techniques of the SVC at the time of clamping The purpose of this study is to assess the efficacy of using a novel technique (external shunt) for decompression of SVC during the time of clamping in comparison with veno-atrial shunt(internal shunt) .