The functional roles of ventricular dominance and additional ventricular chamber after Fontan operation are still uncertain. We aim to assess and correlate such anatomical features to late clinical outcomes.

Fontan patients undergoing cardiac MRI and cardiopulmonary exercise test between January 2020 and December 2022 were retrospectively reviewed. Clinical, cardiac MRI, and cardiopulmonary exercise test data from the last follow-up were analysed.

Fifty patients were analysed: left dominance was present in 29 patients (58%, median age 20 years, interquartile range:16–26). At a median follow-up after the Fontan operation was 16 years (interquartile range: 4–42), NYHA classes III and IV was present in 3 patients (6%), 4 (8%) underwent Fontan conversion, 2 (4%) were listed for heart transplantation, and 2 (4%) died. Statistical analysis showed that the additional ventricular chamber was larger (>20 mL/m2) in patients with a right dominant ventricle (p = 0.01), and right dominance was associated with a higher incidence of post-operative low-cardiac output syndrome (p = 0.043). Left ventricular dominance was associated with a better ejection fraction (p = 0.04), less extent of late gadolinium enhancement (p = 0.022), higher metabolic equivalents (p = 0.01), and higher peak oxygen consumption (p = 0.033). A larger additional ventricular chamber was associated with a higher need for post-operative extracorporeal membrane oxygenation support (p = 0.007), but it did not influence functional parameters on cardiac MRI or cardiopulmonary exercise test.

In Fontan patients, left ventricular dominance correlated to better functional outcomes. Conversely, a larger additional ventricular chamber is more frequent in right ventricular dominance and can negatively affect the early post-Fontan course.