What is PAH?

Pulmonary arterial hypertension (PAH) is a progressive disease that reduces blood flow and increases pressure in the blood vessels of the lung.

What causes PAH?

The pulmonary arteries are the large blood vessels responsible for transporting blood from the heart to the lungs to pick up oxygen. In PAH, the cells lining the inside of these arteries enlarge and multiply. As a result, the arteries thicken, causing resistance to blood flowing through them and so increasing blood pressure. The right side of the heart has to work harder to pump blood through the arteries. This places an increasing strain on the heart, which causes it to enlarge and can lead to right heart failure.1

PAH figure(a) Cross section of a pulmonary artery in a healthy person: the vessel walls are flexible and elastic, allowing blood to pass through easily.

(b) Cross section of a pulmonary artery in a person with PAH: thickening of the vessel creates resistance to blood flow, making it difficult for the heart to pump blood through the lungs.

How many people are affected by PAH?

PAH affects 15–50 individuals per million people.2 People of all ages and ethnic backgrounds suffer from this disease, although it is more common in women than men.3

PAH is defined as ‘Group 1’ in the World Health Organization (WHO) clinical classification of pulmonary hypertension (PH)4 (see classification for further information).

The future for PAH

Although a cure for this life-threatening disease is still some way off, there is much to be optimistic about. An ever-increasing number of treatments are becoming available that improve both quality and length of life for patients with PAH. The present aim is to ensure that all patients with PAH have access to centers of excellence in the diagnosis, management and ongoing treatment of their disease.


  1. Rosenblum WD. Pulmonary arterial hypertension: pathobiology, diagnosis, treatment, and emerging therapies. Cardiol Rev 2010;18:58–63.
  2. Peacock AJ, Murphy NF, McMurray JJ et al. An epidemiological study of pulmonary arterial hypertension. Eur Respir J 2007;30:104–9.
  3. Badesch DB, Raskob GE, Elliott CG et al. Pulmonary arterial hypertension: baseline characteristics from the REVEAL Registry. Chest 2010;137:376–87.
  4. Simonneau G, Gatzoulis MA, Adatia I et al. Updated clinical classification of pulmonary hypertension. J Am Coll Cardiol 2013;62:D34–41.

Further information and educational materials on PAH can be found in the section ‘PH. It’s personal’.

Last updated: February 2, 2015