How Many Hearts Does an Octopus Have?

An octopus has three hearts: two pump blood through the gills, and one main heart circulates it to the rest of the body.

Three. Two branchial hearts feed the gills and one systemic heart serves the body — a setup most people get wrong by guessing just one.

Octopus blood is copper-based and carries oxygen less efficiently, so it needs the extra pumps. The main heart even stops beating when the octopus swims, which is why it prefers to crawl along the seabed.