how many hearts does an octopus have?

An octopus has three hearts. Two of these hearts, called branchial hearts, pump blood to the gills where it picks up oxygen. The third heart, called the systemic heart, pumps the oxygenated blood to the rest of the body. Notably, the systemic heart stops beating when the octopus swims. This three-heart system helps compensate for their blue blood, which uses a copper-based protein (hemocyanin) that is less efficient at carrying oxygen compared to the iron-based hemoglobin in red blood.