Pulmonary arterial hypertension (PAH) is a rare cause of high blood pressure in the lungs. Blood, after giving up its oxygen to the body tissues, is returned through the veins to the right lower heart chamber (right ventricle). The right ventricle then pumps the blood through the lungs to pick up a new supply of oxygen. Blood pressure in the lungs and the right ventricle is normally about one-fifth as much as elsewhere in the body.
When there is increased blood pressure in the lungs, the right ventricle must work harder to pump blood to the lungs. The heart muscle tries to compensate by becoming thicker and stronger. As the disease gets worse, the right ventricle can’t compensate any more and symptoms appear.