Aim: To assess galectin-3 (Gal-3) levels and their relationship with clinical status and right ventricular (RV) performance in adults with RV pressure overload of various mechanisms due to congenital heart disease. Materials & methods: A cross-sectional study was conducted. Patients underwent clinical examination, blood testing and transthoracic echocardiography. Results: The study included 63 patients with congenitally corrected transposition of the great arteries, 41 patients with Eisenmenger syndrome and 20 healthy controls. Gal-3 concentrations were higher in patients compared with controls (7.83 vs 6.11 ng/ml; p = 0.002). Biomarker levels correlated with age, New York Health Association class, N-terminal probrain natriuretic peptide and RV function only in congenitally corrected transposition of the great arteries patients. Conclusion: Gal-3 profile in congenital heart disease patients and pressure-overloaded RV differs according to the cause of pressure overload.