What are the pulmonary veins?

The pulmonary veins are responsible for transporting oxygenated blood from the lungs to the heart (to the left atrium), which is then pumped outward to the rest of the body. Together with the pulmonary arteries, they make up the pulmonary circulation (also called "heart-lung circulation" or "small circulation") or part of the circulatory system. Pulmonary circulation is a part of the cardiovascular system and is responsible for carrying deoxygenated blood and waste products from all the organs and tissues of the body away from the heart, to the lungs, and returning oxygenated blood back to the heart, as well as enriched nutrients to all other organs and tissues.

In the systemic circulation (or “large circulation”) which is the part of the circulatory system responsible for sending oxygenated blood to all other organs and tissues, the arteries are given the task to transport oxygenated blood, while the veins are concerned with the transport of deoxygenated blood and waste products. The system is reversed in the pulmonary circulation, where the pulmonary veins are in fact the only veins in the human body to carry oxygenated blood.

Each pulmonary vein is linked to a network of capillaries (small blood vessels) in the alveoli of each lung. Alveoli are tiny air sacs within the lungs where oxygen and carbon dioxide are exchanged. These capillaries link together to form a single blood vessel from each lobe of the lung. The right lung contains three lobes, while the left contains only two. The pulmonary veins that connect the right lung to the heart are called the right pulmonary veins, while those that connect the heart to the left lung are called left pulmonary veins. There are typically four pulmonary veins, two for each lung.  Depending on the lobe, the left and right pulmonary veins are further divided into upper and lower categories.  


  • Left superior: drains the left upper lobe
  • Left inferior: drains the left lower lobe
  • Right superior: drains the right upper and middle lobes
  • Right inferior: drains the right lower lobe


Characterized by their thin walls and elasticity, pulmonary veins have an average length of 1.5 cm, while in diameter they are between 13 to 16 mm. They do not have valves. Usually, the right pulmonary veins are thicker than those on the left, and they flow into the left atrium near the atrial septum, while the left pulmonary veins flow into the side wall.

Any condition that affects the blood vessels along the course between the heart and lungs is referred to as pulmonary vascular disease. The causes of pulmonary vascular disease generally depend on which of the lungs’ blood vessels are affected. A common symptom includes shortness of breath and seeking treatment is essential in order to determine the most appropriate form of treatment and prevent further complications from arising.


What function do the pulmonary veins serve?  

The most important function of the pulmonary veins is to carry oxygenated blood from the lungs to the heart, which is then pumped outward to the rest of the body. After the blood is carried to other parts of the body via arteries, it loses oxygen and turns into deoxygenated blood. The human body cannot live and grow without oxygen; hence the pulmonary veins are of great significance in this field. They hold the key to proper functioning of the circulatory and cardiovascular system.