Most arteries in the human body carry oxygen-rich (oxygenated) blood, while veins carry oxygen-poor (deoxygenated) blood. But the pulmonary artery is an exception — and patients often get confused when their doctor or test report mentions it.

At Sai Hospital, Haldwani, cardiologists often explain this concept to patients undergoing tests like echocardiography, CT scans, or pulmonary evaluations. This article breaks down in simple terms why the pulmonary artery carries deoxygenated blood, how it functions, and why it is essential for life.

Understanding the Basics: Arteries vs Veins

Before understanding the pulmonary artery, recall the general rule:

• Arteries → carry blood away from the heart
• Veins → carry blood towards the heart

Most arteries carry oxygen-rich blood because they supply the organs.
Most veins carry oxygen-poor blood because they bring used blood back to the heart.

But the pulmonary circulation is different.

What Is the Pulmonary Artery?

The pulmonary artery is the large blood vessel that carries blood from the right ventricle of the heart to the lungs.

Its main job is to deliver blood that is low in oxygen to the lungs so it can pick up fresh oxygen and release carbon dioxide.

Why Does the Pulmonary Artery Carry Deoxygenated Blood?

Because its destination is the lungs, not the body.

The pulmonary artery carries blood away from the heart — fulfilling the definition of an artery — but the blood it carries hasn’t been oxygenated yet.

Let’s understand the process step-by-step:

1. Blood Returns to the Heart After Use

After circulating through the body, blood returns to the heart via:

• Superior vena cava (upper body)
• Inferior vena cava (lower body)

This blood is deoxygenated — meaning it has delivered oxygen to body tissues and picked up carbon dioxide.

2. This Blood Enters the Right Atrium and Right Ventricle

From the vena cavae:
→ blood enters right atrium
→ passes through tricuspid valve
→ enters right ventricle

The right ventricle is designed to pump blood to the lungs.

3. The Pulmonary Artery Carries This Deoxygenated Blood to the Lungs

When the right ventricle contracts, it pushes the blood into the pulmonary artery.

Because this is the only artery that carries deoxygenated blood, it seems like an exception — but it makes perfect sense:

The job of this artery is to transport deoxygenated blood directly to the lungs so it can become oxygenated.

4. Blood Becomes Oxygenated in the Lungs

Inside the lungs:

• Blood releases carbon dioxide
• Blood absorbs fresh oxygen from inhaled air

This gas exchange happens in tiny air sacs called alveoli.

5. Oxygenated Blood Returns to the Heart Through Pulmonary Veins

Once oxygenated, blood travels back to the heart via the pulmonary veins.

This is another exception:

• Pulmonary veins carry oxygenated blood (unlike other veins).

The oxygen-rich blood then enters the left atrium, goes to the left ventricle, and gets pumped throughout the body through the aorta.

Why Is the Pulmonary Artery Different From Other Arteries?

Because its function is different.

Typical arteries:

• Deliver oxygenated blood to organs

Pulmonary artery:

• Delivers deoxygenated blood to the lungs
• Part of the “low-pressure” pulmonary circulation
• Works closely with lung function, not body organs

Its structure is also slightly different — with thinner walls compared to systemic arteries, because it pumps under lower pressure.

Common Misconception: Arteries = Oxygenated Blood

Many people think arteries carry only oxygen-rich blood.
This is incorrect.

Correct rule:

Arteries carry blood away from the heart.
Veins carry blood towards the heart.

Oxygen content varies depending on which side of the heart and which circulation is involved.

Clinical Relevance at Sai Hospital, Haldwani

Understanding pulmonary artery function is important for conditions like:

• Pulmonary hypertension
• Congenital heart defects (e.g., PDA, Tetralogy of Fallot)
• COPD and lung disease
• Pulmonary embolism
• Heart failure
• High blood pressure in lung vessels

Cardiologists often assess pulmonary artery pressure during echocardiography or CT scans to diagnose these conditions accurately.

FAQs: Why Does the Pulmonary Artery Carry Deoxygenated Blood?

1. Why doesn’t the pulmonary artery carry oxygen?
Because it carries blood straight from the right side of the heart to the lungs before oxygenation.

2. Do any other arteries carry deoxygenated blood?
Yes — the umbilical arteries in the fetus also carry deoxygenated blood.

3. Which blood vessel brings oxygen back from the lungs?
The pulmonary veins bring oxygenated blood to the heart.

4. What happens if the pulmonary artery is blocked?
A blockage (pulmonary embolism) can be life-threatening because it stops the blood from reaching the lungs for oxygen.

5. Is the pulmonary artery high-pressure or low-pressure?
It is low-pressure compared to systemic arteries, because the lungs are nearby and require gentle blood flow.

Conclusion

So, why does the pulmonary artery carry deoxygenated blood?
Because its job is to transport oxygen-poor blood from the heart to the lungs so it can pick up oxygen. While it behaves like an artery in direction, it carries deoxygenated blood because it’s part of the lung circulation, not the system-wide circulation.

At Sai Hospital, Haldwani, our cardiologists explain these concepts during patient evaluation so you can better understand your heart and lung health. If you have breathing issues, fatigue, or suspected heart–lung problems, early testing helps protect long-term health.

For appointments or assessments, our team is here to help you breathe easier and live healthier.