PDE5A and hydrops fetalis: Furthermore, the mechanism of idiopathic PH and remodeling might be different from HF-induced PH and remodeling as previous studies clearly demonstrated that the commonly used effective therapies for idiopathic PH (such as PDE5 inhibitors or endothelin receptor antagonists) were not effective in treating HF-induced PH (46), suggesting the underlying mechanisms of these pulmonary vessel remodeling and PH are different.