Pulmonary arterial hypertension (PAH) is a serious condition in which the small arteries in your lungs become narrowed and stiff, forcing your heart to work much harder to pump blood through them. The pressure inside these arteries rises above 20 mmHg (normal is much lower), and over time this extra strain can weaken the right side of your heart. PAH is progressive, meaning it tends to worsen without treatment, but newer therapies have significantly improved outcomes over the past two decades.
How PAH Differs From Regular High Blood Pressure
When most people hear “hypertension,” they think of the blood pressure reading taken at a doctor’s office with an arm cuff. That measures systemic blood pressure, the force in the arteries throughout your body. PAH is entirely different. It refers specifically to elevated pressure in the pulmonary arteries, the vessels that carry blood from the right side of your heart to your lungs to pick up oxygen.
PAH also falls under a broader umbrella called pulmonary hypertension (PH), which has five distinct groups based on the underlying cause. Group 1 is PAH itself, where the problem originates in the lung arteries. Other groups include PH caused by left-sided heart disease, chronic lung conditions like COPD, or blood clots in the lungs. The distinction matters because each group requires a different treatment approach.
What Happens Inside the Lungs
In a healthy person, the walls of the small pulmonary arteries are thin and flexible, allowing blood to flow easily. In PAH, three things go wrong at once. The inner lining of these arteries stops producing enough of the molecules that keep vessels relaxed and open. At the same time, it overproduces signals that cause the vessel walls to tighten and the smooth muscle cells surrounding them to multiply. The result is arteries that are narrower, stiffer, and increasingly obstructed.
Three molecular pathways drive this process. One involves a substance called endothelin-1, which triggers blood vessels to constrict and their walls to thicken. A second involves nitric oxide, a natural vasodilator your body produces less of in PAH. The third is the prostacyclin pathway, which normally helps keep vessels open and prevents harmful cell growth. In PAH, all three pathways are disrupted simultaneously.
As these arteries narrow, the right ventricle (the chamber of the heart that pumps blood to the lungs) faces mounting resistance. Initially it compensates by growing thicker and more muscular, but eventually this adaptation fails. The right ventricle dilates, weakens, and can no longer pump effectively. This progression to right-sided heart failure is the most dangerous complication of PAH.
Symptoms and How They Progress
PAH is often called a “silent” disease in its early stages because the first symptoms are easy to dismiss. The World Health Organization classifies the severity of PAH into four functional classes based on how much activity you can handle before symptoms appear.
- Class I: No limitation in physical activity. You feel fine during normal exertion, and the disease may only be detected through testing.
- Class II: Slight limitation. Ordinary activities like climbing stairs or carrying groceries bring on shortness of breath, fatigue, or chest pain, but you’re comfortable at rest.
- Class III: Marked limitation. Even light activity, less than your normal routine, triggers symptoms.
- Class IV: Symptoms at rest. Signs of right heart failure are present, and fainting episodes can occur.
The most common early symptom is breathlessness during physical activity that seems out of proportion to the effort. Fatigue, dizziness, chest tightness, and a racing heartbeat are also typical. Because these symptoms overlap with so many other conditions, the average time from first symptoms to a correct PAH diagnosis has historically been over a year.
What Causes PAH
PAH has several recognized triggers, though in many cases no clear cause is found (a form called idiopathic PAH). Known causes and associations include connective tissue diseases like scleroderma, congenital heart defects, liver disease, HIV infection, and certain drugs or toxins.
Genetics also play a role. About 75% of heritable PAH cases involve a mutation in a gene called BMPR2, which helps regulate cell growth in blood vessel walls. If you carry this mutation, the lifetime risk of developing PAH is roughly 14% for men and 42% for women. This sex difference is one reason PAH is diagnosed more often in women overall, though the exact hormonal mechanisms remain unclear.
How PAH Is Diagnosed
Diagnosis typically starts with noninvasive tests. An echocardiogram (ultrasound of the heart) can estimate pulmonary pressures and show whether the right side of the heart is enlarged or strained. But the definitive test is right heart catheterization, a procedure in which a thin, flexible tube is threaded through a vein (usually in the neck or groin) into the right side of the heart and pulmonary artery.
This catheter directly measures three critical values: mean pulmonary artery pressure, pulmonary vascular resistance (how much the narrowed arteries resist blood flow), and wedge pressure (an indirect gauge of pressure on the left side of the heart). A PAH diagnosis requires a mean pulmonary artery pressure above 20 mmHg, pulmonary vascular resistance above 2 Wood Units, and a wedge pressure of 15 mmHg or below. That last number is key because it rules out high pressure caused by problems on the left side of the heart, which would point to a different type of pulmonary hypertension entirely.
Treatment Approaches
There is no cure for PAH, but treatment can slow progression, relieve symptoms, and improve quality of life. The medications used target the same three dysfunctional pathways described earlier.
One class of drugs blocks endothelin receptors, preventing endothelin-1 from constricting blood vessels and promoting cell overgrowth. Another class boosts the nitric oxide pathway by preventing the breakdown of a molecule called cGMP, which relaxes smooth muscle in the artery walls. A third group delivers synthetic versions of prostacyclin or stimulates its receptors, helping vessels stay open while also protecting the right heart’s pumping strength. Some patients also respond to calcium channel blockers, which reduce calcium flow into smooth muscle cells and promote relaxation of the vessel walls.
Most people with PAH today are started on combination therapy, using drugs from two or more of these classes simultaneously. This multi-pathway approach has been one of the biggest advances in PAH care over the past decade.
A New Type of Treatment
In 2024, the FDA approved sotatercept, the first drug in an entirely new class for PAH. Unlike the existing medications, which primarily work by relaxing blood vessels, sotatercept targets the underlying cell overgrowth that thickens and remodels the artery walls. It works as a decoy, trapping signaling proteins called activins that drive excessive cell proliferation. By intercepting these signals, sotatercept helps rebalance the growth pathways in pulmonary artery walls. This represents a shift from simply widening narrowed vessels to actually addressing the structural changes that make them narrow in the first place.
Survival and Long-Term Outlook
PAH remains a serious diagnosis, but survival has improved substantially in the modern treatment era. A systematic review of population-based studies found that one-year survival globally ranges from 85% to 99%, three-year survival from 65% to 95%, and five-year survival from 50% to 86%. The wide ranges reflect differences in how early the disease is caught and how advanced it is at diagnosis.
Functional class at the time of diagnosis is one of the strongest predictors of outcome. Among patients diagnosed at an earlier stage (Class I or II), five-year survival was around 76%. For those diagnosed with more advanced symptoms (Class III or IV), that number dropped to roughly 57%. This gap underscores why early detection matters so much. European registry data show one-year survival of about 90% and five-year survival of approximately 61%, while North American data report similar one-year figures around 88%.
Beyond survival, quality of life is a major concern. Exercise tolerance, the ability to work, and daily energy levels are all affected. Treatment goals focus not just on extending life but on keeping patients in lower functional classes where they can remain active and independent for as long as possible.