Fontan circulation and transplantation: Considerations for the complex candidate.

The Fontan operation has transformed survival for patients with single ventricle congenital heart disease, but the long-term durability of this physiology remains limited. Fontan circulatory failure (FCF) is a progressive, heterogeneous condition associated with multiorgan dysfunction, lymphatic failure, and elevated post-transplant risk when not recognized early. With increasing survival into adulthood, heart transplantation has emerged as the definitive "fourth stage" of palliation. However, referrals for advanced therapies are often delayed, with many patients presenting in advanced stages of decline. This review synthesizes current evidence on the pathophysiology of Fontan failure, outlines consensus indications for transplant evaluation, and highlights pre-transplant strategies including management of end-organ dysfunction, collateral embolization, and psychosocial readiness that are essential to optimizing outcomes. Advances in surgical technique and mechanical support has markedly improved post-transplant survival, yet challenges remain in timely referral, equitable access, and transition care. Early recognition and multidisciplinary coordination is key to improving outcomes in this vulnerable and growing population.