How many hearts does the giant Pacific octopus have?

The giant Pacific octopus has three hearts. Two branchial hearts pump blood through the gills, where it receives oxygen, while one systemic heart pumps oxygenated blood to the rest of the body.

This arrangement suits an octopus’s unusual circulation. Its blood contains hemocyanin, a copper-based protein that carries oxygen and appears blue when oxygenated. The giant Pacific octopus lives in cold North Pacific waters, where oxygen transport can be especially important.

The systemic heart pauses while the octopus swims, which helps explain why this species generally prefers crawling along the seafloor. Its two branchial hearts continue supporting gas exchange. When the octopus crawls, the systemic heart works normally.

Having three hearts does not mean the animal has three separate circulatory systems. The hearts work together within one closed circulatory system. Other octopuses and many related cephalopods also have three hearts, so this is a broader cephalopod trait rather than a feature unique to the giant Pacific octopus.