In pediatric cardiac surgery, there is a substantial gap between published recommendations or guidelines for blood product use and clinical practice. The drawbacks of blood transfusion are well acknowledged though. The aim of this paper is to present the rationale for packed red blood cells, fresh frozen plasma (FFP), and platelets used in pediatric patients. Blood hemoglobin level is the current trigger used for packed red blood cells transfusion, though commonly admitted to be suboptimal. An increase in hemoglobin level is likely to be associated with an increase in blood oxygen content and blood oxygen delivery. However, above a critical level of hemoglobin, normovolemic anemia is well tolerated, and any increase in hemoglobin will fail to increase oxygen consumption and therefore to improve end-organ oxygen supply. FFP is one way to address the coagulation factors deficiency induced by hemodilution, consumption, or hepatic insufficiency. The volume needed to increase these factors is not negligible. To avoid dilution and/or fluid overload, the use of clotting factor concentrate is recommended. The same remark can be made regarding the treatment of antithrombin III deficiency. Platelets infusion should be restricted to bleeding patients with thrombocytopenia and without surgical bleeding. In clinical studies, the prevention of bleeding through prophylactic infusion of platelets proved to be useless. Optimizing the use of blood products (avoiding overuse, underuse, and inappropriate use) is a challenging task in pediatric cardiac surgery. Data or guidelines cannot replace clinical judgment and the decision to transfuse is left to individual discretion, but the medical community needs to optimize its transfusion practice, otherwise policy-makers without similar expertise may step in to regulate the use of blood products.