PH is a disease of abnormally high blood pressure in the arteries of the lungs (also known as pulmonary arteries). In PH, the right ventricle (RV, lower chamber on the right side) of the heart has to work harder to pump blood through the lungs. This is because of several factors:

• The pulmonary arteries are narrowed, and some may be closed
• The walls of the pulmonary arteries are thicker and stiffer
• The blood pressure in the pulmonary arteries (also known as pulmonary artery pressure = PAP) is higher

As the RV works harder over time, this strain on the RV leads to the muscle of the RV getting thicker and stronger (also known as RV hypertrophy). In order for the thicker muscle (hypertrophy) of the RV to pump enough blood, it needs to be filled with more blood. This causes a back-up of blood into the right atrium (RA, upper chamber on the right side), and also behind the heart.

This back-up of blood behind the heart can be examined by your doctor:

• You may have a higher pressure in the jugular vein of the neck (also known as higher JVP = jugular venous pressure)
• You may have a swollen, enlarged, and tender liver, which can make you feel sick to your stomach (also known as nausea) or lose your appetite
• You may have swelling of the belly with fluid (also known as ascites)
• You may have swelling of the feet/ankles (also known as edema)

Because the RV has to work harder in PH, eventually, the RV gets weaker, and cannot pump enough blood for the body. This is known as RV failure, a type of heart failure. Patients with RV failure:

• Can feel extremely tired
• Can feel chest pain, especially on effort or exertion
• Can feel faint or lightheaded, especially on effort or exertion
• Can lose consciousness or pass out (also known as syncope)

If PH is not treated, many PH patients may eventually develop RV failure. In patients with RV failure, the risk of death can be very high, if therapy is not begun.