Introduction. The use of thyroid hormone supplementation (THS) for donor optimization has not been standardized and remains an area of academic investigation and clinical interest. The purpose of this study is to investigate the impact of THS supplementation on heart transplant recipient outcomes. Methods. Adult heart transplant recipients in the UNOS database recorded from January 1, 2000 to June 30, 2022 formed the study cohort. Simple comparisons were made with t-tests or chi-squared tests. Logistic regression models were used to predict 30 day and 1 year survival. Accelerated failure time models were employed to analyze time to death and time to rejection. Results. The cohort consisted of 46,542 heart transplants, of which 28,911 (62%) received THS prior to organ procurement. In adjusted models, donor THS was associated with a reduction of 11% in the odds of death within 30 days (OR = 0.89; p=0.048); however, this relationship did not extend to one year post-transplant survival (OR = 1.00; p=0.968). After a sex-based analysis, 30-day survival benefit was seen only in male-to-male donor-recipient pairings (OR for death = 0.82; p=0.007). Overall survival and post-transplant rejection was also improved in the male-to-male group (HR = 0.94; p=0.002 and HR = 0.96; p=0.048) and the female-to-female group (HR = 0.87; p=0.003 and HR = 0.90; p=0.013). There was no associated survival benefit with THS in sex mismatched groups. Conclusion. THS in donors is associated with improved 30-day post-transplant survival and overall survival after OHT in sex-matched donor-recipient pairs. Further study is warranted.