Pulmonary hypertension is abnormally high blood pressure in the arteries of the lungs. It makes the right side of the heart need to work harder than normal.

Normally, the left side of the heart produces a high blood pressure in order to pump blood to the body. The right side of the heart pumps blood through the lungs under much lower pressure.

Pulmonary hypertension is usually caused by a narrowing of the small arteries of the lung. This narrowing makes it harder for the right side of the heart to circulate the blood to the lungs. Over time, the right side of the heart may become enlarged and een fail (cor pulmonale).

Pumonary hypertension may be caused by:

• A genetic defect
• Any condition that causes chronic low oxygen levels in the blood
• Autoimmune diseases, such as scleroderma
• Certain diet medications
• Congestive heart failure
• History of a blood clot in the lung
• HIV infection
• Lung or heart valve disease
• Obstructive sleep apnea

In many cases, the cause is unknown, in which case the condition is known as idiopathic pulmonary arteril hypertension (IPAH).

If it is caused by a known medicine or medical condition, it is called secondary pulmonary hypertension.

IPAH is rare. It affects more women than men.