How many hearts does an octopus have?

An octopus has three hearts. Two branchial hearts pump blood through the gills, while a larger systemic heart sends oxygenated blood around the body.

This arrangement suits an animal whose blood uses copper-rich hemocyanin to carry oxygen. Hemocyanin is less efficient than the iron-based hemoglobin found in humans, so the octopus relies on a dedicated pump at each gill to help oxygenate its blood.

The systemic heart is two-chambered and receives oxygenated blood from the gills before distributing it through the body. The two branchial hearts work together, one beside each gill. Their coordinated rhythm supports the octopus’s closed circulatory system.

A surprising detail is that the systemic heart temporarily stops during strenuous jet-propelled swimming. This helps explain why many octopuses prefer crawling, although they can swim rapidly when escaping danger. The same animal also has blue blood because of its hemocyanin.