Pulmonary hypertension is high blood pressure in the arteries that supply blood to the lungs. The causes are varied and can be divided into five main groups. **Group 1: Pulmonary Hypertension Due to Conditions Involving the Lungs or Airway Disease** Causes include: * Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) * Interstitial lung disease * Emphysema **Group 2: Pulmonary Hypertension Caused by Left-Sided Heart Disease** Causes include: * Left-sided heart valve disease, such as mitral valve or aortic valve disease * Failure of the lower left heart chamber (left ventricle) **Group 3: Pulmonary Hypertension Caused by Lung Disease** Causes include: * Chronic obstructive pulmonary disease (COPD) * Scarring of the tissue between the lung's air sacs (pulmonary fibrosis) * Obstructive sleep apnea * Long-term exposure to high altitudes in people who may be at higher risk of pulmonary hypertension **Group 4: Pulmonary Hypertension Caused by Chronic Blood Clots** Causes include: * Chronic blood clots in the lungs (pulmonary emboli) * Other clotting disorders **Group 5: Pulmonary Hypertension Triggered by Other Health Conditions** Causes include: * Blood disorders, including polycythemia vera and essential thrombocythemia * Inflammatory disorders such as sarcoidosis and vasculitis * Metabolic disorders, including glycogen storage disease * Kidney disease * Tumors pressing against pulmonary arteries **Eisenmenger Syndrome and Pulmonary Hypertension** Eisenmenger syndrome is a type of congenital heart disease that causes pulmonary hypertension. It's most commonly caused by a large hole in the heart between the two lower heart chambers (ventricles), called a ventricular septal defect. This hole in the heart causes blood to flow incorrectly in the heart. Oxygen-carrying blood (red blood) mixes with oxygen-poor blood (blue blood). The blood then returns to the lungs — instead of going to the rest of the body — increasing the pressure in the pulmonary arteries and causing pulmonary hypertension. **Risk Factors** Pulmonary hypertension is more often diagnosed in people ages 30 to 60. Growing older can increase the risk of developing Group 1 pulmonary hypertension, called pulmonary arterial hypertension (PAH). However, PAH from an unknown cause (idiopathic PAH) is more common in younger adults. Other things that can raise the risk of pulmonary hypertension include: * A family history of the condition * Being overweight * Blood-clotting disorders or a family history of blood clots in the lungs * Exposure to asbestos * Congenital heart disease * Living at a high altitude * Use of certain drugs, including some weight-loss medicines and illegal drugs such as cocaine or methamphetamine * Use of selective serotonin reuptake inhibitors (SSRIs), used to treat depression and anxiety **Complications** Potential complications of pulmonary hypertension include: * Right-sided heart enlargement and heart failure (cor pulmonale) * Blood clots * Irregular heartbeats (arrhythmias) * Bleeding in the lungs * Pregnancy complications