Octopuses, or octopi, are one of the most well-known animals with multiple hearts. They have three hearts: one central heart to pump blood throughout their circulatory system, and two peripheral or branchial hearts to pump blood through their gills.
Much like octopi, squids also have three hearts. These hearts serve similar functions: one pumps blood throughout the body, and two pump blood over the gills. Squids can be found in every ocean, with some species growing to enormous sizes.
Earthworms have five primitive "hearts" called aortic arches. These structures help to pump blood around their bodies and contribute to their role as decomposers, improving soil quality. Earthworms are widespread and can be found in almost every habitat with soil.
Despite being famous for their slime production, hagfish have one main heart and three supplementary heart-like structures. These hearts help them survive in oxygen-poor water by pumping for up to 36 hours without oxygen.
Cuttlefish, like octopi and squids, have three hearts: one for pumping blood throughout the body and two for pumping blood over the gills. Cuttlefish are found worldwide, with some species exhibiting high levels of intelligence.
Cockroaches have 13 chambers in their heart, acting similarly to hearts. This unique arrangement makes them extremely resilient creatures, able to survive in harsh conditions and with severe injuries. Cockroaches are found worldwide, with some species being well-known household pests.
Horses have one actual heart and four heart-like structures called frogs, one at the bottom of each foot. These frogs act as blood reservoirs, pumping blood into the horse's arteries with each step. So, in a way, every horse has five "hearts."