BACKGROUND: The Karnofsky Performance Scale (KPS) is widely used to assess functional status in heart transplantation (HT) candidates and inform risk stratification. However, its subjective nature raises questions about the consistency and prognostic value of KPS scoring across centers. METHODS: We analyzed adult patients undergoing first-time single-organ HT from November 2018 to June 2024 in the United Network for Organ Sharing database. Patients with prior transplants, multi-organ transplants, missing data, or loss to follow-up before 1 year were excluded. KPS at transplantation was analyzed continuously and categorized as low (0-30), medium (40-70), or high (80-100). Hierarchical linear and logistic regression models with center-level random effects were used to assess variability in KPS assignment and the association between KPS and 1-year posttransplant mortality. RESULTS: Among 13 726 patients, median KPS at transplantation was 30 (IQR 20-50), and 60% were in the low range. Adjusted hierarchical linear models showed 28% (95% CI 22%-33%) of KPS variance was attributable to differences between centers. KPS was not associated with 1-year mortality (OR 1.00, 95% CI 0.99-1.00; p = 0.564), and no between-center heterogeneity in this association was detected. CONCLUSION: KPS exhibits substantial center-level variability and is not associated with 1-year mortality in heart transplantation, suggesting caution in using KPS for short-term risk stratification.