Adult congenital heart disease (ACHD) often leads to increased blood flow in the pulmonary circulation resulting in pulmonary arterial hypertension (PAH), which is associated with increased patient morbidity and mortality. According to the 2020 European Society of Cardiology (ESC)/European Respiratory Society (ERS) guidelines, PAH is present when the mPAP is greater than 20 mmHg and PVR is greater than 3 WU (pre-capillary pulmonary hypertension). The most common classification of ACHD-PAH patients is in four groups depending on the defect type, shunt direction, and history of congenital heart disease surgical correction. The Bosentan Randomized Trial of Endothelin Antagonist Therapy-5 (BREATHE-5) showed that bosentan is effective in treating patients with Eisenmenger Syndrome, whereas the more recent Macitentan in Eisenmenger Syndrome to Restore Exercise Capacity (MAESTRO) Study concluded that Macitentan has a neutral effect on the same population. Treatment of patients with ACHD-PAH should be individualized and carried out in specialized centers.