What is PAH? Pulmonary arterial hypertension is a specific type of pulmonary hypertension caused when the tiny arteries in the lung become thickened and narrowed. This blocks blood flow through the lungs, raising the blood pressure in the lungs and causing the heart to work harder. In the early stages of PAH, it is possible a patient may not notice any symptoms at all. As the disease progresses, they will start to experience symptoms common to other lung diseases. The most common symptoms include:
