Kuwata S, et al. - Whether thyroid function is impaired and contributes to perturbed hemodynamics in patients after Fontan operation, was investigated in this study including 37 patients who underwent a Fontan operation. These subjects underwent cardiac catheterization and blood tests for thyroid function. Subclinical thyroid dysfunction with an elevated thyroid-stimulating hormone (TSH) level despite normal thyroxine levels was detected in 12 patients (33%). Findings revealed a significant correlation of TSH levels with central venous pressure. A remarkably elevated γ-glutamyltransferase level, an indicator of liver congestion, was detected in patients with subclinical hypothyroidism (SCH) vs other patients (125.6±12.2 vs 67.6±4.6 IU/L). Based on the findings, thyroid dysfunction is possibly attributable to venous congestion in Fontan patients, which could lead to decreased ventricular function and cardiac output in these subjects. Routine monitoring of thyroid function after Fontan surgery was recommended.