Therefore—in ACHD patients without worsening symptoms of heart failure or recent hospitalizations—we aimed to assess the following: (1) The prognostic value of plasma Gal-3 levels and systemic ventricle (SV) GLS, (2) The association of plasma Gal-3 levels with GLS of the systemic ventricle, (3) The association of plasma Gal-3 levels and GLS with supraventricular and ventricular arrhythmias, (4) The association of plasma Gal-3 levels with NTproBNP, an established prognostic marker in ACHD patients. Here, LGALS3 is linked to heart failure.