Pulmonary hypertension is a condition caused by high blood pressure that affects the arteries in the lungs and right side of the heart. There are different forms of pulmonary hypertension, and it occurs when arteries become narrow or blocked. This makes blood flow more difficult, which raises blood pressure and forces the heart to pump harder. This leads to weakened heart muscles and possible heart failure. Signs include chest pain, fatigue, fainting and swelling. Treatments are specific to the type and case, and include oxygen therapy and blood thinners.