Background The physiologic hallmarks of the Fontan circulation—chronically elevated central venous pressures and low cardiac output—have significant effects not only on cardiovascular status but also impact other organ systems. Exercise capacity is limited in many and declines with age, accelerating in adolescence, but with wide variability. We explore the relationship between exercise performance and end‐organ function in outpatient subjects with a Fontan circulation. Methods and Results This is a cross‐sectional analysis of subject end‐organ characterization from our outpatient Fontan circulation clinic with peak oxygen consumption (peak V o 2 ) at cardiopulmonary exercise testing as the primary outcome. We perform linear regression to assess associations between clinical characteristics and peak V o 2 as well as the magnitude of the association of clinical characteristics with peak V o 2 . Of 265 subjects age 12.8 (9.5–16.4) years, there is a negative correlation between age and peak V o 2 (−0.49, P o 2 . Variables positively associated with peak V o 2 and their effect size include vitamin D sufficiency (+3.00, P =0.020) and absolute lymphocyte count (+0.23, P =0.005). Status as overweight/obese (−3.91, P =0.003) and hemoglobin (−0.77, P =0.003) are negatively associated. Neither ventricular morphology, timing of Fontan palliation, nor Fontan circulation type affect peak V o 2 . Conclusions Higher peak V o 2 in those with a Fontan circulation is associated with younger age, vitamin D sufficiency, absence of overweight/obese, lower hemoglobin, and a healthier hepatic profile. Whether exercise training or other initiatives can modify organ characteristics in those with a Fontan circulation is worthy of exploration.
