This proposed research provides an interdisciplinary approach to understanding exercise intolerance by examining cardiac and musculoskeletal metabolism in a unique cohort of children with congenital heart disease. Study findings may more importantly lead to evidence-based exercise interventions that promote improvements in overall physical health, quality of life, and functional status for Fontan children. Furthermore, this pilot study will lead to the development of a novel research protocol which may be applied to larger Fontan and other congenital heart disease cohorts. This study will also provide preliminary data to develop and conduct a larger clinical research project.