Blood in the pulmonary veins is oxygen-rich and bright red, while blood in almost all other veins is oxygen-poor and darker red. Pulmonary veins bring this oxygenated blood from the lungs back to the left side of the heart, whereas other veins return deoxygenated blood from body tissues to the right side of the heart.

Quick Scoop

Pulmonary veins are a special case in the circulation system and behave more like arteries in terms of the kind of blood they carry. They are among the only veins in the body that carry oxygenated blood instead of deoxygenated blood.

Key differences in the blood

  • Pulmonary venous blood has high oxygen and low carbon dioxide because it has just passed through the lungs where gas exchange occurred.
  • Blood in other systemic veins has low oxygen and high carbon dioxide because it has already delivered oxygen to tissues and picked up waste gases.
  • Pulmonary venous blood is brighter red, while venous blood from the rest of the body is a darker shade of red due to lower oxygen saturation.

Where the blood is going

  • Pulmonary veins carry blood from the lungs to the left atrium, ready to be pumped out through the aorta to the whole body.
  • Other veins (like the superior and inferior vena cava) carry blood from the body back to the right atrium so it can be sent to the lungs for reoxygenation.

A small extra detail

  • Pulmonary venous blood is not usually 100% saturated with oxygen, because a tiny amount of deoxygenated bronchial venous blood can mix into pulmonary veins before they reach the heart.
  • Even with this small mixing, pulmonary venous blood still has the highest oxygen content of any blood entering the heart, which is why it is crucial for supplying the body’s organs.

Information gathered from public forums or data available on the internet and portrayed here.