Pulmonary arterial hypertension (PAH) is a group of diseases characterized by elevated pulmonary arterial resistance leading to right heart failure. PAH is progressive and potentially fatal. PAH may be idiopathic and/ or familial, or induced by drug or toxin (drug-or toxin-induced PAH, see these terms) or associated with other diseases like congenital heart disease, connective tissue disease, HIV, schistosomiasis, portal hypertension (PAH associated with other disease, see this term).