Increased blood pressure in the blood vessels leading from the heart to the lungs.

With pulmonary arterial hypertension, the blood vessels to the lungs develop an increased amount of muscle in the wall of the blood vessels. This muscle creates a narrowing of the blood vessels, which causes the blood not to flow as it should, resulting in less oxygen in the blood.

Underlying causes include high blood pressure in the lungs’ arteries due to some types of congenital heart disease, connective tissue disease, coronary artery disease, high blood pressure, liver disease (cirrhosis), blood clots to the lungs, and chronic lung diseases like emphysema. Genetics also plays a role.