BackgroundPatient reported outcome measures (PROMs) correlate with heart failure (HF) severity among adults and are adjunct tools in clinical care. Limited data exist regarding the validity of PROMs in pediatric HF. Hypothesis: Patient Reported Outcome Measurement Information System® (PROMIS®) Pediatric Fatigue correlates with HF severity, measured by the New York University Pediatric Heart Failure Index (NYU PHFI). MethodsChildren ≥8 and <18 years old were enrolled prospectively at 4 hospitals, 09/2019 - 02/2023, while receiving inpatient HF care. NYU PHFI and pediatric self-report PROMIS measures were administered inpatient and outpatient. PROMIS measures: Mobility, Anxiety, Depressive symptoms, Peer relationships and Fatigue (primary outcome). Paired t-tests compared PROMIS and NYU PHFI scores across time. A mixed effects model generated correlation coefficients. ResultsIn the 41-patient cohort, twenty (48.8%) were discharged without VAD/transplant,18 completed inpatient and outpatient assessments. Mean PROMIS Fatigue t-scores improved: 58.1±12.9 to 48.9±16.9; p=0.007. Clinically meaningful improvements were observed in other PROMIS t-scores, except Peer Relationships. NYU PHFI scores improved: 13.3±2.6 to 7.8±3.4; p<0.001. PROMIS Fatigue and NYU PHFI moderately correlated (r = 0.5; 95% CI 0.3, 0.6). ConclusionsPROMIS Fatigue t-scores moderately correlated with HF severity in children suggesting that Fatigue could be useful in longitudinal monitoring and in clinical trials.