Pulmonary arterial hypertension (PAH) is a serious disease of the arteries connecting the lungs to the heart (the pulmonary arteries). Under normal conditions, the right side of the heart (the right atrium and right ventricle) pumps venous blood through the lungs, so the blood can pick up oxygen.
When PAH develops, blood flow through the pulmonary arteries is restricted, and the right side of the heart is put under increasing strain to pump blood through to the lungs.
These changes in the blood vessels raise the pressure and increase the resistance to blood flow through the lungs, making it harder for the heart to pump blood through the lungs. Over time, due to the additional strain, the heart begins to work less effectively and eventually, the right heart can fail (this is known as 'right ventricular failure').
Common symptoms of PAH include breathlessness, fainting, fatigue, chest pain, chest tightness, palpitations, limited exercise capacity, and swollen ankles and legs.