Learn About Pulmonary Arterial Hypertension | American Lung Association

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Learn About Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is one form of a broader condition known as pulmonary hypertension, which means high blood pressure in the lungs. PAH occurs when the very small arteries throughout the lungs narrow in diameter, which increases the resistance to blood flow through the lungs. Over time, the increased blood pressure can damage the heart.

Key Facts

  • Pulmonary arterial hypertension (PAH) is a specific type of pulmonary hypertension where the tiny blood vessels in the lungs become scarred.
  • The symptoms of PAH are common to other diseases which makes it more difficult to diagnose.
  • PAH is a complex condition that will usually worsen without the right treatment.

What Is Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is high blood pressure in the lungs. PAH can be present even if you have normal “regular” (systemic) blood pressure because the blood vessels in the lung are very different from the blood vessels in the rest of the body. PAH is a specific type of pulmonary hypertension that is caused by the development of scar tissue in the tiny blood vessels of the lung. This scar tissue blocks the blood flow through the lungs and causes the pressure in those blood vessels to increase.

How Pulmonary Arterial Hypertension Affects Your Body

The heart and the lungs work together to deliver nourishing oxygen-rich blood throughout the body. The left side of the heart receives blood with high oxygen content from the lungs, and pumps it through the body via arteries. Oxygen is taken up by cells of the muscles and organs, and the low oxygen content blood is collected in the veins and returned to the right side of the heart. The right side of the heart pumps this blood back to the lungs where it picks up oxygen again.

Normally, the pressure in the right side of the heart and the blood vessels of the lungs is lower than in the rest of the body. This allows the blood to collect as much oxygen as possible while in the lungs. In someone with PAH, the scarred and narrowed blood vessels in the lungs make it harder for the blood to get through. This forces the right side of the heart to pump harder, under greater pressure. If this increased pressure is not treated, it can cause the right side of the heart to become overworked and possibly fail. This problem can also reduce the ability of the blood to collect enough oxygen to keep the body functioning normally.

How Serious Is Pulmonary Arterial Hypertension?

Pulmonary arterial hypertension is a very serious disease. It is not the same as other, more common forms of pulmonary hypertension, which are usually caused by other underlying diseases of the heart, lungs, or other organs. PAH is a rare condition, affecting about 15-50 people per million in the US. Since patients with PAH are often not diagnosed until their symptoms are severe, they may only have a few years to live unless they get proper treatment. Fortunately, advances in therapies have led to impressive improvements for patients with pulmonary arterial hypertension.


    This content was developed in partnership with the CHEST Foundation, the philanthropic arm of the American College of Chest Physicians.


    Approved by Scientific and Medical Editorial Review Panel. Last reviewed August 4, 2016.

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