How many hearts does an octopus have?

The Three-Hearted Wonder of the Ocean

Octopuses are genuinely alien creatures, and their cardiovascular system is one of the best examples of just how different they are from us. While you're running on a single heart, an octopus keeps itself going with three — each with a distinct and critical job to do.

How the Three Hearts Work

Two of the hearts are called branchial hearts, and they sit at the base of each of the octopus's two gills. Their sole purpose is to pump blood through the gills, where it picks up oxygen from the surrounding water. Think of them as dedicated gill pumps.

The third heart — the systemic heart — then takes that freshly oxygenated blood and pumps it out to the rest of the body: the organs, the muscles, the brain, and all eight arms. It's the main distributor, the central hub of the whole operation.

Why Does It Need Three?

The answer lies in octopus blood itself. Instead of hemoglobin (the iron-based protein that makes human blood red), octopuses use hemocyanin, a copper-based protein. Hemocyanin is significantly less efficient at carrying oxygen than hemoglobin, especially at warmer temperatures. To compensate, octopuses evolved a system that keeps blood moving efficiently through multiple pumping stages, making sure enough oxygen reaches their active, energy-hungry bodies.

There's a fascinating trade-off, though. When an octopus swims using jet propulsion — shooting water through its mantle — the systemic heart actually stops beating during the motion. That's why octopuses prefer crawling along the seafloor to open-water swimming; sustained swimming is genuinely exhausting for them because of this cardiac pause.

Blue Blood and Cold Efficiency

Hemocyanin also gives octopus blood its striking blue color. It's not a quirk — it's chemistry. Copper binds with oxygen differently than iron does, producing that distinctive hue. In cold, low-oxygen environments like deep water, hemocyanin actually outperforms hemoglobin, which is one reason cephalopods like octopuses thrive in colder ocean depths.

Three Hearts, Nine Brains

The three-heart system is just one piece of the octopus's remarkable biology. They also have nine brains — one central brain and a smaller neural cluster in each arm that processes information independently. Combined with three hearts and blue blood, it's hard not to see why marine biologists often describe octopuses as the closest thing on Earth to a genuinely alien intelligence.

So next time you picture an octopus drifting through a coral reef, remember: there are three hearts beating inside that soft, boneless body, keeping one of nature's most extraordinary minds alive and hunting.