What are the pulmonary arteries?

The pulmonary arteries carry blood from the right side of the heart to the lungs. In medical terms, the word “pulmonary” means something that affects the lungs.

The blood carries oxygen and other nutrients to your cells. Your heart is the muscle pump that drives the blood through your body. The heart has four chambers, right atrium, right ventricle, left atrium and left ventricle. The deoxygenated blood returns from the body to the right atrium and from there enters the right ventricle that pumps it to the lungs through the main pulmonary artery (pulmonary trunk). In the lungs, the blood refills its oxygen supply and gets rid of carbon dioxide.

The oxygenated blood returns from the lungs to the left atrium through the pulmonary veins to the heart. The left ventricle then pumps this oxygen-rich blood throughout the body.

What are the parts of the pulmonary arteries?

The pulmonary arteries are part of the pulmonary circulation and play a critical role in oxygenating blood and removing carbon dioxide.

They are made up of three layers:

  • Intima, a smooth inner layer.
  • Media, a middle layer that pushes blood through.
  • Adventitia, a protective outer layer.

What role do the pulmonary arteries play in the circulatory system?

The pulmonary arteries work with other parts of your heart to help blood circulate through your lungs. Here’s how:

  • Right ventricle: The heart’s bottom right ventricle (chamber) sends oxygen-poor blood into the main pulmonary artery (pulmonary trunk).
  • Pulmonary valve: The pulmonary valve (pulmonic valve) is one of four heart valves —“gates” that open and close to secure forward blood flow. The pulmonary valve opens to let oxygen-poor blood flow out of the heart and into the pulmonary arteries on its way to the lungs for oxygen. When closed, the pulmonary valve keeps blood from flowing backward into the heart (pulmonary valve regurgitation).
  • Pulmonary arteries: The main pulmonary artery or pulmonary trunk divides after it exits the heart’s bottom right ventricle. The right pulmonary artery branch goes to the right lung. The left branch goes to the left lung. From here, the pulmonary arteries divide into many smaller blood vessels and eventually reaches the capillaries surrounding the alveoli where the gas exchange takes place.
  • Pulmonary veins: The veins do the opposite job of pulmonary arteries and collects the oxygenated blood and carry it from the lungs back to the heart. The veins merge into larger veins. Each lung has two pulmonary veins that deliver blood to the heart’s top left chamber or atrium.
  • Left atrium: This atrium sends oxygenated blood into the heart’s bottom left ventricle.
  • Left ventricle: The bottom left chamber of the heart pumps oxygen-rich blood back out to your body. After having passed through the tissue and delivered the oxygen, the systemic veins collect the blood and brings it back to the right heart and then the cycle begins again.

Common Conditions & Disorders

What conditions and disorders affect the pulmonary arteries?

The most common problems with the pulmonary arteries are congenital heart defects, meaning the issue is present at birth. To understand these defects you have to understand a little about the development of the heart and the circulation before you are born. Normal development of the heart and pulmonary arteries requires that the two sides of the heart shares the work equally and the way that happens is that there are two communications between the pulmonary and the systemic circulation, one atrial (foramen) and one between the pulmonary artery and the aorta (ductus). Disturbed balance result in problems. These communications normally close soon after birth.

  • Pulmonary artery stenosis: The pulmonary trunk or pulmonary artery branches are too narrow, making it difficult for blood to travel to the lungs and get oxygen. This problem is often combined with other defect, most commonly a ventricular septal defect. As a result, the heart’s lower right ventricle (chamber) works harder to pump blood. The heart muscle thickens, leading to an enlarged heart. Pulmonary artery stenosis is usually congenital. Less commonly, infections or heart procedures cause the condition in adults.
  • Pulmonary valve stenosis: This heart defect is also congenital. It causes a thickened or stiff pulmonary valve. Sometimes, the valve’s flaps or leaflets fuse together. A thickened, stiff or fused pulmonary valve can’t completely open. The heart works harder to move blood through the valve, causing the heart to enlarge.
  • Pulmonary hypertension (PH): This type of high blood pressure affects the lungs. Pulmonary hypertension occurs when arteries in the lung thicken and narrow. Blood flow slows from the pulmonary arteries to the lungs. Congenital heart defects (e.g an one ductus) and left heart valve and muscle diseases can cause PH. Your heart works harder to move blood through the pulmonary arteries, increasing pressure on the arteries.
  • Pulmonary valve regurgitation: Regurgitation is another word for leaky heart valves. It occurs when blood flows backward from the pulmonary artery into the heart’s lower right ventricle (chamber). Pulmonary valve regurgitation is rare. It is most often the result of previous surgeries for congenital pulmonary stenosis but occasionally secondary to pulmonary hypertension. There are also hormone producing tumors in the gut (carcinoid) that may make the valve shrink and cause leak. It may lead to an enlarged heart (hypertrophic cardiomyopathy) or heart failure.
  • Pulmonary embolism: A pulmonary embolism is a potentially life-threatening blood clot in the lungs. It occurs when a blood clot in the leg, arm or another part of the body (often a deep vein thrombosis) breaks free and travels to a lung. The clot lodges in a pulmonary artery or vein. It can obstructs the pulmonary arteries and cause heart damage and can be fatal.
  • Pulmonary artery aneurysm: Rarely, part of the pulmonary artery wall weakens. This weakened area can widen or balloon out. It is very unusual that these aneurysms rupture, causing a life-threatening problem. That really only happens if the patient also has pulmonary hypertension. Congenital heart defects may cause a pulmonary aneurysm, but they aren’t common.

Any of these conditions can be associated with arrhythmias and cause heart failure.

Caring for Your Heart and Pulmonary Arteries

How can I protect my heart and pulmonary arteries?

Many of the conditions that affect the pulmonary arteries are present at birth. While you can’t prevent these problems, these actions can promote better heart health:

When should I talk to a doctor?

You should call your healthcare provider if you experience:

A note from Cleveland Clinic

Your pulmonary arteries play an important role getting carbon dioxide out of your blood and oxygen back into it. Many conditions that affect the pulmonary arteries and pulmonary blood circulation are congenital or present at birth. But coronary artery disease and other heart disease can damage the pulmonary arteries. Depending on the heart problem, you may need surgery or other treatments to improve blood flow and oxygenation. Your healthcare provider can offer suggestions on ways to improve your heart health.

Last reviewed by a Cleveland Clinic medical professional on 03/10/2021.


  • Adult Congenital Heart Association. Pulmonary Hypertension. (https://www.achaheart.org/your-heart/health-information/pulmonary-hypertension/) Accessed 3/10/2021.
  • American Heart Association. Problem: Pulmonary Valve Regurgitation. (https://www.heart.org/en/health-topics/heart-valve-problems-and-disease/heart-valve-problems-and-causes/problem-pulmonary-valve-regurgitation) Accessed 3/10/2021.
  • Castaner E, Gallardo X, Rimola J, et al. Congenital and acquired pulmonary artery anomalies in the adult: (https://pubs.rsna.org/doi/full/10.1148/rg.262055092) Radiologic overview. RadioGraphics. Accessed 3/10/2021.
  • Kreibich M, Siepe M, Kroll J, et al. Aneurysms of the pulmonary artery. (https://www.ahajournals.org/doi/full/10.1161/circulationaha.114.012907) Circulation. 2015;131:310-16. Accessed 3/10/2021.
  • Tucker WB, Weber C, Burns B. Anatomy, thorax, heart pulmonary arteries. (https://www.ncbi.nlm.nih.gov/books/NBK534812/) StatPearls (Internet). 2020. Accessed 3/10/2021.

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