Octopuses have three hearts

Three Hearts? Octopuses Really Are That Extra

Yes, octopuses genuinely have three hearts — and once you understand why, it makes perfect sense for one of the ocean's most remarkable creatures.

How the Three-Heart System Works

Two of the hearts are called branchial hearts, and they sit on either side of the octopus's body, one next to each gill. Their sole job is to pump deoxygenated blood through the gills, where it picks up oxygen from the surrounding water.

The third heart — the systemic heart — sits in the centre and takes over from there. It pumps the now-oxygenated blood out to the rest of the body: the muscles, the organs, the brain, and all eight arms.

It's essentially a two-stage pumping system, engineered to keep oxygen moving efficiently through a body with a very unusual layout.

Blue Blood and a Different Kind of Chemistry

Here's where it gets even more interesting. Octopus blood is blue. Not metaphorically — literally blue, because it uses a copper-based molecule called haemocyanin to carry oxygen, rather than the iron-based haemoglobin found in human red blood cells.

Haemocyanin is less efficient at carrying oxygen than haemoglobin under warm, stable conditions — but it performs remarkably well in cold, low-oxygen environments like the deep ocean. The three-heart system helps compensate for that lower efficiency by keeping the blood moving under higher pressure.

There's a Catch — Swimming Exhausts Them

Despite this impressive cardiac setup, octopuses actually tire out quickly when they swim. That's because the systemic heart — the central one — stops beating when an octopus swims, leaving the oxygen delivery system temporarily compromised. This is why octopuses strongly prefer crawling along the seafloor to jet-propelled swimming. It's not laziness; it's cardiovascular logistics.

Nine Brains to Go with Three Hearts

If three hearts weren't enough, octopuses also have nine brains — a central brain plus a small cluster of neurons in each of the eight arms, allowing each limb to act semi-independently. Pair that with their three-hearted circulatory system, and you start to appreciate just how differently evolution can solve the problem of building a complex, intelligent animal.

A Design Built for the Deep

The octopus's triple-heart system isn't a biological quirk — it's a finely tuned solution to the challenges of being a soft-bodied, cold-water predator with high oxygen demands and no skeleton to help circulate fluids. Every element of their biology connects to every other.

So next time someone calls something "overcomplicated," maybe just say: three hearts, nine brains, blue blood. Octopuses have been over-engineering brilliance for roughly 300 million years.