Inclusion Criteria:  Congenital heart patients (2.5 - 15kg) have consented for a planned cardiac surgery procedure requiring cardiopulmonary bypass. Parent or legal substitute decision-maker informed written consent to participate in the study.  Exclusion Criteria:  Patient or family refusal to participate. Patient over 15kg (Fontan or Glenn patients will be considered up to 18kg) No planned use of cardiopulmonary bypass Isolated ASD repair Known severe hematologic abnormality such as sick cell anemia, thalassemia, haemophilia A or B, von Willebrand disease or other. Known genetic syndrome with severe neurologic or multi-organ abnormalities and immune dysfunction such as DiGeorge Syndrome, Trisomy 18 or 13, Noonan syndrome. (Trisomy 21 may be included in the study). Known immunodeficiency syndrome or bone marrow pathology. Severe liver or renal disease.