Could a doctor please give me info on pulmonary hypertension?

PAH: Pulmonary Arterial Hypertension is a rare and a serious illness, affects the arteries of the lungs. The vessels became narrow, it makes the heart to work harder to push the blood throughout the lungs. As the disease progress, it leads to the right sided heart failure. There are several causes of PAH: idiopathic ( or unknown), hereditary, connective tissue diseases, drugs, toxins,infections.