Fontan failure has been variably and inconsistently described in the literature, leading to challenges in comparing studies and evaluating treatments. Development of a conceptual framework to describe clinical phenotypes will aid in consistent terminology in the literature. In the heart failure literature, several key concepts have been described-"heart failure" is a clinical syndrome of various etiologies, with phenotype-specific response to therapies. As the congenital heart disease community struggles to grapple with "Fontan failure," these concepts come to light. Fontan failure in the context of four clinical phenotypes, including evaluation, potential management strategies, and future directions is discussed.