Repair of pediatric congenital heart defects on cardiopulmonary bypass presents a variety of challenges to the perfusionist, generally correlating with the complexity of the defect. While all pediatric perfusion inherently requires techniques that differentiate it from those used in adult perfusion, complex congenital defects require additional considerations. These include an understanding of the cardiac defect and its effects on blood flow, the physiologic requirements of children, and employing techniques to maintain physiologic equilibrium while minimizing volume administration and the need for transfusion. This chapter will discuss the general principles guiding perfusion practice in congenital heart diseases (CHDs), as well as the advanced techniques that are essential in managing these cases.