Background: Fontan physiology results in multiorgan dysfunction, most notably affecting the liver and kidney. We evaluated the utility of Model for End-Stage Liver Disease Excluding INR (MELD-XI) score, a score evaluating the function of both liver and kidney to identify Fontan patients at increased risk for morbidity and mortality post–heart transplant. Methods: The Pediatric Heart Transplant Society database was queried to identify Fontan patients listed for heart transplant between January 2005 and December 2018. MELD-XI scores were calculated at listing and heart transplant. A multivariable analysis was conducted to identify risk factors for post–heart transplant mortality. Demographic, clinical characteristics, and survival differences were evaluated and compared between the high and low MELD-XI score cohorts. The impact of changing MELD-XI scores during the waitlist period on post–heart transplant outcomes was also evaluated. Results: Of 565 Fontan patients who underwent transplantation, 524 (93%) had calculable MELD-XI scores at the time of heart transplant: 421 calculable at listing and 392 calculable at listing and at heart transplant. On multivariable analysis, only MELD-XI score (squared) (hazard ratio, 1.007), history of protein-losing enteropathy (hazard ratio, 2.1), and ventricular assist device use at transplant (hazard ratio, 3.4) were risk factors for early phase post–heart transplant mortality. Patients with high MELD-XI scores at heart transplant had inferior survival post–heart transplant (P = .02); those in the high MELD-XI score cohort at wait listing and heart transplant tend to have the worst post–heart transplant survival; however, this was not significant (P = .42). Conclusions: The MELD-XI, an easily calculated score, serves as a valuable aid in identifying pediatric Fontan patients at increased risk for post–heart transplant mortality.