The Biology of the Octopus Heart: Three Pumps and Blue Blood

The Octopus is often described as the closest thing to an alien intelligence on Earth. It has a brain distributed throughout its eight arms, no bones, and the ability to change the color and texture of its skin in milliseconds.

But its internal plumbing is just as strange. To manage its complex biology in the cold, high-pressure depths of the ocean, the octopus does not rely on a single, centralized pump. It requires Three Separate Hearts and a completely different type of blood.

The Three Pumps

A single, central heart is highly efficient for mammals. But the octopus body plan—essentially a sack of organs connected to eight massive, highly active arms—requires a more decentralized approach.

The Systemic Heart: This is the main, central pump. Its only job is to take oxygen-rich blood and pump it at high pressure out to the brain and the eight arms.
The Branchial Hearts (x2): Located right next to each of the octopus's two gills are two smaller "Branchial" hearts.

The Flow

When the oxygen-poor blood returns from the arms, it has lost all its pressure. Instead of making the main heart do all the work, the two Branchial Hearts grab this sluggish blood and forcefully pump it through the gills to pick up fresh oxygen. The freshly oxygenated blood is then handed off to the Systemic Heart to be fired back into the body.

The Hemocyanin Limit: Blue Blood

Why does the octopus need such an aggressive, three-stage pumping system? Because its blood is terrible at carrying oxygen.

Hemoglobin (Iron): Human blood is red because we use Iron to bind oxygen. Hemoglobin is incredibly efficient at grabbing and releasing oxygen quickly.
Hemocyanin (Copper): The octopus, evolving in the deep, cold ocean, uses Copper to bind oxygen. This copper-based protein is called Hemocyanin. When it binds to oxygen, the blood turns a brilliant, striking Blue.

The Stamina Problem

Hemocyanin is much larger and significantly less efficient at releasing oxygen into the tissues than hemoglobin. It works well in the freezing, low-oxygen abyss, but it makes the octopus a terrible endurance athlete.

The Sprint: An octopus can sprint very fast to escape a predator (using jet propulsion).
The Collapse: However, a fast sprint instantly drains the inefficient blue blood of its oxygen. Worse, the high pressure required for jet propulsion physically squeezes the Systemic Heart so hard that it stops beating entirely while the octopus is swimming fast.

This means an octopus cannot swim fast for more than a few seconds. It must stop, rest on the bottom, and let its three hearts catch up and push the sluggish blue blood back through its gills. This is why octopuses prefer to slowly crawl along the ocean floor rather than swim.

Conclusion

The Octopus is a master of rapid problem-solving and sudden, violent ambush. But its endurance is strictly limited by the copper in its veins. By evolving three separate hearts, it attempts to overcome the inefficiency of its own blue blood, proving that evolution often relies on sheer mechanical force to compensate for chemical limitations.

Scientific References:

Wells, M. J. (1983). "Circulation in cephalopods."
O'Dor, R. K., & Webber, D. M. (1986). "The constraints on cephalopods: why squid aren't fish." Canadian Journal of Zoology. (Context on the stamina limits).
Ghiretti-Magaldi, A., et al. (1985). "Hemocyanins."