Post-transplant de novo anti-HLA donor specific antibodies (DSA) indicate a worse outcome in adult transplantation. No large prospective studies have established the prevalence of newly detected DSA after pediatric heart transplant (HT), nor studied their impact on outcomes. We used the CTOTC-04 cohort to determine the incidence, specificity and time course of newly detected DSA in the 1st yr post-HT.