Clinical Study Assessing the Efficacy and Safety of Macitentan in Fontan-palliated Subjects

Inclusion Criteria: * Written informed consent/assent from the subject and/or a legal representative prior to initiation of any study-mandated procedures * Fontan-palliated subjects with either intra-atrial lateral tunnel total cavopulmonary connection (LT-TCPC), or extra cardiac tunnel TCPC (EC-TCPC) surgery \> 1 year before Screening. Either LT- or EC-TCPC can be primary or secondary to atrio-pulmonary connection * New York Heart Association (NYHA) functional class (FC) II or III (assessed by the investigator using the Specific Activity Scale * Women of childbearing potential must have a negative serum pregnancy test use reliable contraception Exclusion Criteria: * Pattern of Fontan circulation severity * Deterioration of the Fontan-palliated condition. * Limitations to Cardiopulmonary exercise testing (CPET) * Peak VO2 \< 15 mL/kg/min. * Any known factor or disease that may interfere with treatment compliance or full participation in the study