Pulmonary hypertension (PH) is the result of a process that begins with changes in the cells that line your lungs’ arteries. This process includes three types of changes that affect the pulmonary arteries:

* The walls of the arteries tighten.
* The walls of the arteries are stiff at birth or become stiff from an overgrowth of cells.
* Blood clots form in the arteries.

These changes make it hard for the heart to push blood through the arteries and into the lungs. Thus, the pressure in the arteries rises, resulting in PH.

A number of different factors can contribute to the process that leads to the different types of PH.

Group 1 pulmonary arterial hypertension (PAH) may have no known cause, or it may be inherited (passed from parents to children through the

genes). Certain diseases and conditions, such as congenital heart disease, HIV, and thyroid disease, also can cause this type of PH. Also, the use of certain diet medicines and street drugs (such as cocaine) can lead to this type of PH.

Many different diseases and conditions can lead to the development of groups 2 through 5 PH (often called secondary PH), including:

* Mitral valve disease
* Lung conditions, such as COPD (chronic obstructive pulmonary disease)
* Sleep apnea
* Sickle cell anemia
* Sarcoidosis

For more information about the types of PH and the diseases, conditions, and factors that can contribute to PH, see “Types of Pulmonary Hypertension.”