Why Octopuses Have Three Hearts
An octopus has three hearts because its body needs extra pumping power to move oxygen through its blood, which carries oxygen far less efficiently than ours. One main heart (the systemic heart) pumps oxygen-rich blood to the whole body, while two smaller gill hearts push blood through the gills so it can pick up oxygen from the water.
What makes this so unusual is octopus blood itself: it is blue, not red. Instead of iron-rich haemoglobin, octopuses use a copper-based molecule called haemocyanin to carry oxygen, and copper turns the blood blue. Haemocyanin is a weaker oxygen carrier, so the two gill hearts help make up for it.
Learners meet a few surprising ideas here — that a heart is simply a pump, that blood is a delivery system for oxygen, and that different animals have solved the same problem in very different ways. One curious fact stands out: when an octopus swims, its main heart stops beating, which tires it quickly, so it usually prefers to crawl along the seabed instead.
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Meet the octopus🐙 An octopus has THREE hearts! You have just one heart beating in your chest. But an octopus swimming deep in the ocean has three — all beating at the same time! ❤️ 💜 💜 One big heart + two smaller helper hearts Why would an animal need so many hearts? Let's dive in and find out. 🌊
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What a heart doesFirst, what is a heart? A heart is a pump. It squeezes to push blood around the body. Blood is like a delivery van — it carries oxygen (the "air" our bodies need) to every part. Squeeze… release… squeeze… — that's a heartbeat. 💡 No oxygen = no energy. Every animal needs a way to move oxygen around, and hearts do that job.
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Tap the three heartsThe three hearts & their jobs Tap each glowing heart to discover what it does. See if you can find all three! Tap a heart above to reveal its secret job. 👆 0 of 3 hearts found
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The two gill heartsTwo hearts just for the gills The two purple hearts are called gill hearts. Their only job is to push blood through the gills — the octopus's underwater "lungs" that grab oxygen from the water. Give the gill hearts a hand! Tap the pump button to send blood through the gills and fill them with oxygen. 💜 → 🌊 → gills → 🫧 Pumps: 0 / 8 Pump the gill hearts 💜 💡 More gills to feed = more pumping needed. Two extra hearts make sure the gills always get plenty of blood.
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Blue bloodA surprise: blue blood! Your blood is red because of iron. But octopus blood is blue! It uses a special copper-based helper called haemocyanin to carry oxygen. The catch: blue blood is not very good at carrying oxygen, especially in cold, deep water. Tap to see why that matters. 👇 Why does weak blue blood matter? 🔎 …
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The swimming mysteryThe strangest fact of all When an octopus swims, something odd happens: its main heart stops beating! That's why octopuses get tired quickly and prefer to crawl along the seabed instead. 🤔 Quick think: With blue blood that carries little oxygen AND a main heart that pauses when swimming, why might THREE hearts be so helpful for an octopus? So it can beat the other sea animals in a race To move enough oxygen around, since its blood and swimming make that hard Because three is its lucky number
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Match the heartsMatch each heart to its job Tap a job word, then it will jump to the heart it belongs to. Fill both slots! Pumps blood to the whole body Pushes blood through the gills ❤️ Main heart (1 of these)drop the job here 💜💜 Gill hearts (2 of these)drop the job here
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You did it!🐙🎉 You're an octopus expert! Here's the amazing story of the three hearts: 1 main heart pumps oxygen-rich blood to the whole body. 2 gill hearts push blood through the gills to pick up oxygen from the water. Octopus blood is blue and carries oxygen weakly — so extra hearts help move enough of it. The main heart stops when swimming, so octopuses would rather crawl. 🌟 Three hearts are the octopus's clever trick for staying full of energy in the deep, cold sea. Nature is full of surprises — keep asking "why"!
Frequently asked questions
- Why do octopuses have three hearts instead of one?
- Two hearts (the gill hearts) push blood through the gills to collect oxygen from the water, and the third (the main or systemic heart) pumps that oxygen-rich blood around the rest of the body. The extra hearts help because octopus blood carries oxygen less efficiently than human blood.
- Why is octopus blood blue?
- Octopus blood uses a copper-based molecule called haemocyanin to carry oxygen, and copper makes the blood look blue. Human blood is red because it uses iron-rich haemoglobin instead.
- What does the main heart of an octopus do differently from the gill hearts?
- The main (systemic) heart pumps oxygen-rich blood to the whole body, while the two gill hearts only push blood through the gills so it can pick up oxygen. They work together as a team.
- Is it true an octopus's heart stops when it swims?
- Yes — the main heart stops beating while an octopus swims, which is why swimming tires it out quickly. For this reason, octopuses usually prefer to crawl along the seabed.
- What are gills and why does an octopus need hearts for them?
- Gills are the octopus's underwater 'lungs' that take in oxygen from the water. The two gill hearts pump blood through them so the blood can collect oxygen before the main heart sends it around the body.
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