Alloantibodies in Pediatric Heart Transplantation

Inclusion Criteria: * All participants listed for heart transplantation at participating CTOT-C study sites. Exclusion Criteria: * Listed for multiple organ transplant * Inability or unwillingness of the participant or parent/guardian to give written informed consent or comply with the study protocol * Condition or characteristic which in the opinion of the investigator makes the participant unlikely to complete at least one year of follow-up * Current participation in other research studies that would, or might, interfere with the scientific integrity or safety of current study (e.g. by interference with immunosuppression management guidelines, study endpoints, excessive blood draws or SAE evaluation).