It is not always known what causes PAH or what the best treatment is. The doctors doing this study would like to understand more about why some people develop PAH and other do not. They also would like to learn more about which treatments might help PAH and which people might respond better to treatments.

Doctors think that testing certain substances found in blood cells might help answer these questions. These substances are normally released by our bodies to protect us from infection and to tell the difference between normal and foreign substances in our body. Finally, a new test will study very small molecules called microRNA that control how our genes are expressed. This study is being done to see if blood samples can be tested to determine who might develop PAH, how well drugs will work to treat PAH and to learn more about the development of PAH.

You will be asked to donate blood when you have your right heart catheterization and also at the 3-4 month follow-up visit. The amount of blood collected during your heart catheterization is about 20cc (about 4 teaspoons). This blood is discarded as part of the clinical catheterization procedure, but we are asking that we use it for this research study. Then, at the follow-up right heart catheterization, you will be asked to donate 20 cc (which is about 4 teaspoons) of blood.

If the second right heart is not required for clinical purposes then you will be asked to give a blood sample during your 3-4 month follow up clinic visit.

If you require an additional right heart catheterization, within one year, we will ask that you donate additional samples at the subsequent RHC.

Other data collected as part of your clinical care, such as medical history, chest x-ray (picture of your lungs), echocardiogram (picture of your heart), ventilation perfusion scan (determines how much blood goes to your lungs), chest CT (thin pictures of my lungs as slices), pulmonary function tests (breathing tests), and lab blood tests, will be used as part of this research.

Inclusion Criteria:

• ≥ 18 years of age
• Not pregnant
• Undergoing right heart catheterization for PAH diagnosis

Exclusion Criteria:

• Pregnant

We expect to enroll 200 patients, who have been referred to the Pulmonary Hypertension Clinic at the Ohio State University Medical Center, in this study. Patients who are ≥ 18 years of age, not pregnant, and undergoing right heart catheterization for PAH diagnosis as part of their clinical care will be approached for consent and participation in this study.