Regarding the potential correlation between the preoperative levels of ET-1 and TGF-β with clinical symptoms of patients with CTEPH awaiting surgical correction, it was curious to notice the lack of correlation between the preoperative levels of both ET-1 and TGF-β and the hemodynamic parameters evaluating the degree of severity of pulmonary hypertension in patients presenting with severe functional limitations (WHO class III and IV). Here, EDN1 is linked to pulmonary arterial hypertension.