Our data are surely peculiar as we were able to confirm, on the one hand, the tight correlation, in patients suffering from CTEPH, between the preoperative values of plasma ET-1 levels and the severity of pulmonary hypertension [6], and, on the other hand, we were also able to show an original finding that the TGF-β production seemed to not be directly associated with the increased intravascular pressure. The gene discussed is EDN1; the disease is chronic thromboembolic pulmonary hypertension.