Acute rejection is an important cause of morbidity and mortality in the pediatric heart transplant (HT) population. A reliable noninvasive method for diagnosis of clinical rejection could substantially reduce these negative outcomes. Evaluate left ventricular (LV) global longitudinal strain (GLS), and global circumferential strain (GCS) as early noninvasive indicators of acute pediatric HT rejection. An 18-month prospective cohort study involving 61 patients evaluated absolute change in peak global systolic strain (GLS and GCS) from enrollment (baseline) to next planned clinical encounter (follow-up) or rejection. Acute rejection defined as a biopsy of grade ≥ 2R or treatment with enhanced immunosuppression by the transplant team, blinded to strain analysis. Two patient cohorts three months post HT without evidence of rejection at enrollment were identified. The study cohort experienced rejection. The control cohort remained free from rejection on follow-up. Two-way analysis of variance (ANOVA) models evaluated change in GLS and GCS by cohort group and time. Applying exclusion criteria, 51 patients enrolled in the control cohort and 10 in the study cohort. The study cohort's mean GLS declined 33% from baseline to rejection (P < .001) and mean GCS declined 16.6% (P = .021). No significant change from baseline to follow-up was seen in the control cohort. A threshold absolute GLS value of 16.1% identified acute rejection with 100% sensitivity and 98% specificity (Likelihood Ratio, [LR] 51). Noninvasive global longitudinal strain was sensitive and specific in the identification of acute clinical rejection in pediatric HT recipients. © 2019 Wiley Periodicals, Inc.