Octopuses are some of the ocean’s most fascinating creatures. One of their coolest features is that they have three hearts, not just one like humans. Two of these hearts work hard to pump blood through their gills, where the blood picks up oxygen from the water. The third heart pumps this oxygen-rich blood to the rest of the body. This setup helps octopuses get enough oxygen to support their active, clever lives even though their blood works differently from ours. Their blood is blue, not red, because it uses a copper-based protein called hemocyanin to carry oxygen, while human blood uses iron-based hemoglobin. Hemocyanin isn’t as good at carrying oxygen, especially in warm water, so octopuses need extra help from their three hearts. Interestingly, the main heart that pumps blood to the body actually stops beating when the octopus swims, which is why octopuses prefer to crawl instead of swim—they get tired fast! This three-heart system is a perfect example of how evolution gave octopuses exactly what they need to survive in their underwater world.
“Octopuses have three hearts because their blue, copper-based blood isn’t as good at carrying oxygen as our red, iron-based blood, so they need extra help pumping it around.”
Reflect
If an octopus’s main heart stops when it swims, how might this shape everything it does—from hunting to hiding? What might this teach us about how animals evolve to fit their worlds?
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Octopuses have three hearts because their blue blood needs extra pumping to carry enough oxygen through their bodies.
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Octopuses have a special circulatory system with three hearts. Two of these hearts are called branchial hearts, and their job is to send blood to the gills. The gills are where the blood picks up oxygen from the water. Then, the third heart, called the systemic heart, pumps this oxygen-rich blood to the rest of the octopus’s body. This division of labor helps the octopus get enough oxygen to its muscles and organs, supporting its active lifestyle underwater.
Unlike humans, whose blood is red due to iron-based hemoglobin, octopuses use hemocyanin to transport oxygen. Hemocyanin contains copper, which turns blue when it binds to oxygen. This blue blood works better in cold, low-oxygen ocean environments but isn’t as efficient as hemoglobin at carrying oxygen, especially in warmer water. Because of this, octopuses need more hearts to pump blood quickly enough to meet their oxygen needs.
When an octopus swims, its systemic heart actually takes a break and stops beating. This means oxygenated blood doesn’t circulate to the body during swimming, so the octopus quickly gets tired. That’s why octopuses prefer to crawl along the ocean floor using their arms—it’s less tiring. This unique heart function shapes how octopuses move and hunt, favoring quick bursts of energy and camouflage over long swims.
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Octopuses have a special circulatory system with three hearts. Two of these hearts are called branchial hearts, and their job is to send blood to the gills. The gills are where the blood picks up oxygen from the water. Then, the third heart, called the systemic heart, pumps this oxygen-rich blood to the rest of the octopus’s body. This division of labor helps the octopus get enough oxygen to its muscles and organs, supporting its active lifestyle underwater.
One source, not peer-reviewed. Thinner than the score suggests.
Supporting passage
Octopuses have a special circulatory system with three hearts. Two of these hearts are called branchial hearts, and their job is to send blood to the gills. The gills are where the blood picks up oxygen from the water. Then, the third heart, called the systemic heart, pumps this oxygen-rich blood to the rest of the octopus’s body. This division of labor helps the octopus get enough oxygen to its muscles and organs, supporting its active lifestyle underwater.
Citations (1 of 2 survived verification)
What limits this
Unlike humans, whose blood is red due to iron-based hemoglobin, octopuses use hemocyanin to transport oxygen. Hemocyanin contains copper, which turns blue when it binds to oxygen. This blue blood works better in cold, low-oxygen ocean environments but isn’t as efficient as hemoglobin at carrying oxygen, especially in warmer water. Because of this, octopuses need more hearts to pump blood quickly enough to meet their oxygen needs.
One source, not peer-reviewed. Thinner than the score suggests.
Supporting passage
Unlike humans, whose blood is red due to iron-based hemoglobin, octopuses use hemocyanin to transport oxygen. Hemocyanin contains copper, which turns blue when it binds to oxygen. This blue blood works better in cold, low-oxygen ocean environments but isn’t as efficient as hemoglobin at carrying oxygen, especially in warmer water. Because of this, octopuses need more hearts to pump blood quickly enough to meet their oxygen needs.
Citations (1 of 2 survived verification)
What limits this
When an octopus swims, its systemic heart actually takes a break and stops beating. This means oxygenated blood doesn’t circulate to the body during swimming, so the octopus quickly gets tired. That’s why octopuses prefer to crawl along the ocean floor using their arms—it’s less tiring. This unique heart function shapes how octopuses move and hunt, favoring quick bursts of energy and camouflage over long swims.
Scored as if sourced, but every citation failed verification.
NO SURVIVING CITATION
Supporting passage
When an octopus swims, its systemic heart actually takes a break and stops beating. This means oxygenated blood doesn’t circulate to the body during swimming, so the octopus quickly gets tired. That’s why octopuses prefer to crawl along the ocean floor using their arms—it’s less tiring. This unique heart function shapes how octopuses move and hunt, favoring quick bursts of energy and camouflage over long swims.
Citations (0 of 2 survived verification)
Nothing openable. Every citation was removed by provenance validation.
What limits this
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Branchial Hearts Pump to Gills
Blood Picks Up Oxygen
Systemic Heart Pumps Oxygenated Blood
Systemic Heart Stops During Swimming
3
Number of hearts
Two branchial hearts and one systemic heart
2/3
Neurons outside the brain
Many neurons are in the arms, showing how complex octopus biology is
4x
Lower oxygen carrying efficiency
Hemocyanin carries oxygen about a quarter as well as human hemoglobin
Humans
Octopuses
Some crustaceans
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From a scientific point of view, the three-heart system in octopuses is an elegant solution to the challenges of their environment. Their copper-based blood protein requires extra help to move oxygen efficiently. Having two hearts dedicated to sending blood to the gills ensures oxygen pickup is fast, while the main heart pumps oxygen-rich blood to the body to power their complex movements and intelligence. The fact that the systemic heart stops during swimming shows how evolution shaped their behavior and physiology for energy conservation.
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