A muscular organ that pumps blood throughout the body, sustaining circulation through rhythmic contraction; in the Human body it consists of two atria and two ventricles.
An Octopus's systemic Heart stops beating whenever it swims. Because the heart that drives blood through the whole body pauses during each jet, octopuses tire fast in open water. That's why many prefer to crawl along the seafloor instead of swimming long distances.
The Octopus has three hearts. Two branchial hearts each push blood through one of its two gills to load it with oxygen, while a third systemic heart circulates the oxygen-rich blood through the rest of the body. The trio is thought to make up for the low efficiency of its blue blood.