Pediatric cardiac surgical patients are at particular risk for post-cardiopulmonary bypass hemorrhage. Moreover, both the incidence and volume of blood transfusions have been associated with increased morbidity in pediatric cardiac patients. Transfusion of red blood cells, platelets, and coagulation factors is necessary to combat the hemodilution associated with cardiopulmonary bypass and to treat postoperative bleeding. We are challenged to apply new pharmacologic, extracorporeal, and laboratory testing advances in an evidence-based, systemic fashion to allow for appropriate transfusion. Transfusion algorithms may aid in this process, but current evidence for efficacy of transfusion algorithms in this population is limited to single-center studies. Development of a transfusion algorithm for the pediatric cardiac population requires individualization at both the institutional level, considering local resources, equipment, and case mix, and the patient level, considering age, cardiac diagnosis, and planned procedure, at minimum. A growing body of literature suggests that application of appropriate intraoperative testing (platelet count, fibrinogen concentration, thromboelastometry) along with recognition of risk factors for bleeding, adequate bypass anticoagulation, and judicious use of factor concentrates allows for thoughtful transfusion and potentially improved outcomes in pediatric cardiac patients. This review examines the evolution of transfusion algorithms in pediatric cardiac surgery and examines the considerations involved in building an algorithm for this challenging, heterogenous population.