Pulmonary Veins

What are pulmonary veins?

Pulmonary veins are blood vessels that carry oxygen-rich blood from your lungs to your heart.

Your pulmonary veins are part of your body’s pulmonary circuit. This is a system of blood vessels that moves blood between your heart and your lungs. This circuit also includes your pulmonary arteries.

What is the difference between the pulmonary veins and the pulmonary arteries?

Your pulmonary veins and pulmonary arteries have two main differences:

• They carry different types of blood. Your pulmonary arteries carry oxygen-poor blood. Your pulmonary veins carry oxygen-rich blood.
• They travel in different directions. Your pulmonary arteries carry blood from your heart to your lungs. Your pulmonary veins carry blood from your lungs to your heart.

What makes pulmonary veins different from other veins?

Your pulmonary veins are the only veins in your body that carry oxygen-rich blood. All your other veins carry oxygen-poor blood.

Similarly, your pulmonary arteries are the only arteries that carry oxygen-poor blood. All the rest of your arteries carry oxygen-rich blood.

As you can see, the pulmonary circuit is a unique part of your body! Your blood vessels in this circuit are the exceptions to the rules about the type of blood each vessel carries.

But one aspect remains the same. That’s the direction of travel. Your pulmonary veins, like all your other veins, carry blood toward your heart. And your pulmonary arteries, like all your other arteries, carry blood away from your heart.

How many pulmonary veins are there?

Most people (60% to 70%) have four pulmonary veins. Everyone else has either three or five pulmonary veins. These changes in number don’t cause any health problems. They’re simply anatomical variations (differences from what scientists consider “normal”) that some people are born with.

What is the function of the pulmonary veins?

Your pulmonary veins collect oxygen-rich blood from your lungs and carry it to your heart. From there, your heart sends the blood to all your other organs and tissues.

Your heart gets a lot of credit for being your body’s pumping powerhouse. And it should. But it can be easy to forget about the blood vessels that enable your heart to pump that blood. If your pulmonary veins suddenly stopped doing their job, your heart wouldn’t receive freshly oxygenated blood to send out to the rest of your body.

So, your pulmonary veins play an essential role in helping your heart do its job. In turn, your pulmonary veins help keep your entire body working.

Where are the pulmonary veins located?

Your pulmonary veins are located between your lungs and your heart. Many smaller blood vessels converge in each of your lungs (right and left) to form a pair of pulmonary veins. Each pair leaves its respective lung through a spot known as the hilum, or root. From there, your pulmonary veins travel to your heart and connect with your left atrium. This is the top left chamber of your heart.

What is the structure of the pulmonary veins?

Most people have four pulmonary veins, with two connected to each lung (right and left):

• Right superior pulmonary vein: Drains your right lung’s upper lobe and middle lobe.
• Right inferior pulmonary vein: Drains your right lung’s lower lobe.
• Left superior pulmonary vein: Drains your left lung’s upper lobe and your lingula (often called the “tongue” in your left lung).
• Left inferior pulmonary vein: Drains your left lung’s lower lobe.

“Superior” means above, and “inferior” means below. So, the name of each vein describes which lung it drains and how it’s positioned.

Normally, each pulmonary vein connects directly with your left atrium. In that case, there are four ostia (openings) in your left atrium, one for each of your pulmonary veins. Oxygen-rich blood travels through these openings and into your left atrium. From there, your blood moves into your left ventricle, which pumps it out to your body through your aorta.

What anatomical variations affect the pulmonary veins?

There are several possible variations of the normal pulmonary vein structure. Some variations affect the number of pulmonary veins you have and how they enter your left atrium. These are healthy and harmless variations.

Other variations prevent your pulmonary veins from draining properly into your left atrium. These variations interfere with your heart’s normal functioning and can be life-threatening.

Harmless variations

About 38% of people have harmless anatomical variations in pulmonary vein structure. These variations affect how many pulmonary veins they have and how those veins connect with their left atrium. These variations include:

• Common left-sided trunk. This means your two left pulmonary veins converge into a shared trunk that connects with your left atrium. So, instead of draining separately into your left atrium, your two left pulmonary veins merge before reaching your left atrium. They then drain their blood together through one opening, rather than two. This common left-sided trunk may be either “short” or “long.” A short left-sided trunk is the most common variation overall, affecting about 15% of people.
• Accessory right pulmonary vein. This means you have an extra (accessory) right pulmonary vein that drains separately into your left atrium. So, instead of two right pulmonary veins, you have three. There are many subtypes within this main category.

These variations are still healthy, and your veins work as they should. That’s because these variations still allow for oxygen-rich blood to enter your left atrium. From there, it can follow the normal path into your left ventricle and then out to the rest of your body.

Variations that interfere with heart function

Some variations prevent your pulmonary veins from bringing oxygen-rich blood to your left atrium. As a result, your heart can’t function as it should.

These variations arise as congenital heart defects. They’re usually diagnosed soon after birth but diagnosis can occur into adulthood as well. They include:

• Total anomalous pulmonary venous return (TAPVR). Babies with TAPVR have pulmonary veins that don’t connect with their left atrium. Instead, their pulmonary veins connect with their right atrium. Their pulmonary veins may drain directly into their right atrium, or they may drain into other veins that connect with their right atrium. Either way, oxygen-rich blood that should enter the left side of their heart instead mixes with oxygen-poor blood on the right side of their heart. And the left side of their heart is closed out of the pulmonary circuit. This is a form of cyanotic heart disease that needs surgery.
• Partial anomalous pulmonary venous return (PAPVR). Babies with PAPVR have at least one pulmonary vein connected to their left atrium. So, some oxygen-rich blood can pass through their aorta and out to their body. These babies still may need treatment, but their condition usually isn’t as critical.

In the U.S., about 1 in 7,809 babies are diagnosed with TAPVR. It’s not clear exactly how many babies are born with PAPVR. But estimates show PAPVR may affect 1 in 143 people, and it occasionally goes unnoticed until adulthood.

Babies with TAPVR or PAPVR usually have a hole between their top two heart chambers (atrial septal defect). This defect is actually life-saving because it allows blood to travel from the baby’s right atrium to their left atrium, and then out to their body. This blood doesn’t contain as much oxygen as it should, but it’s still enough to keep the baby alive until treatment.

How big are the pulmonary veins?

The diameter of a healthy pulmonary vein ranges from 9 to 13 millimeters. Your pulmonary veins vary in diameter as they travel from your lungs to your heart. In general, veins gets wider as it approaches your heart. Your left inferior pulmonary vein is the exception to this rule. It starts out wider as it leaves your left lung and gets narrower as it reaches your heart.

What are pulmonary veins made of?

Three layers of tissues and fibers make up all your veins, including your pulmonary veins. These layers include:

• The tunica adventitia (outer layer), which gives structure and shape to your vein.
• The tunica media (middle layer), which contains smooth muscle cells that allow your vein to widen or narrow as blood comes through.
• The tunica intima (inner layer), which has a lining of smooth endothelial cells. This lining allows blood to flow easily through your vein.

Unlike other veins in your body, your pulmonary veins are partly covered by a thin myocardial layer. This is a “sleeve” of heart muscle tissue that covers a portion of each pulmonary vein near its connection with your left atrium. The average length of this sleeve is 9 millimeters. Your superior pulmonary veins have longer sleeves than your inferior pulmonary veins.

What are common conditions that affect the pulmonary veins?

Conditions that can affect your pulmonary veins include:

• Partial anomalous pulmonary venous return (PAPVR), in which one or more pulmonary veins aren’t connected to your left atrium. PAPVR is usually diagnosed in babies, but occasionally in adults.
• Pulmonary vein obstruction, which involves a blockage in one of your veins. It’s usually caused by a tumor in your heart or lungs that extends to one of your pulmonary veins.
• Pulmonary vein stenosis, which is a narrowing of one or more veins. In babies, it’s often caused by congenital heart defects that affect blood flow. In adults, this condition is sometimes a complication of catheter radiofrequency ablation, which is a treatment for atrial fibrillation.
• Pulmonary vein thrombosis, which is a blood clot in your vein. It typically occurs in people who have lung cancer or who receive a lung transplant.
• Pulmonary venous hypertension, which is raised blood pressure in your pulmonary veins. It’s usually caused by left-sided heart failure. Other causes include cardiac tumors and mitral valve stenosis.
• Total anomalous pulmonary venous return (TAPVR), in which none of your pulmonary veins connect with your left atrium. TAPVR is usually diagnosed soon after birth.

What role do the pulmonary veins play in atrial fibrillation?

Atrial fibrillation (A-Fib) is an abnormal heart rhythm that begins in your pulmonary veins. It may also begin at their junction with your left atrium. Any of your pulmonary veins may trigger A-Fib, but your left superior pulmonary vein is most often involved.

Healthcare providers use a catheter-based procedure called pulmonary vein isolation to treat A-Fib.

What tests check the health of the pulmonary veins?

Providers use several different imaging tests to check your pulmonary veins. These include:

• Chest X-ray.
• Echocardiography.
• MRI.
• CT scan.

How can I take care of my pulmonary veins?

If you’ve been diagnosed with a pulmonary vein condition, it’s important to follow your healthcare provider’s guidance. Many pulmonary vein problems stem from other medical conditions. These need careful treatment and monitoring. Ask your provider what you can do at home to manage your condition and reduce any symptoms.

A note from Cleveland Clinic

Your pulmonary veins carry oxygen-rich blood from your lungs to your heart. They’re essential workers that help keep your body going strong. If you have a heart or lung condition that affects your pulmonary veins, talk with your provider about your prognosis.