9 Animals With Multiple Hearts and the Science Behind Their Extra Pumps
October 24, 2026
A human heart beats roughly 100,000 times a day, and most of the animal kingdom gets by with that same single-pump arrangement. Yet a surprising number of species never settled for just one heart. Some animals with multiple hearts evolved extra pumps because their blood is too thick to move with a single organ, while others needed a separate circuit just to push blood through gills.
The nine creatures below range from backyard earthworms to deep-sea cephalopods, and the reasons behind their extra hearts are stranger than most lists admit. A few of these animals do not actually have “hearts” in the traditional sense at all, which makes the real anatomy more interesting than the popular trivia version. For contrast, it helps to know that some animals get by with no heart whatsoever, relying on currents and body movement instead.
1. Octopus
The common octopus (Octopus vulgaris) is the animal most people picture first when they hear “multiple hearts,” and for good reason. Octopuses contain three hearts: one systemic heart, and two branchial hearts. The systemic heart pumps blood around the octopus’s body, while its two branchial hearts pump blood through its two gills.
The reason comes down to blood chemistry. Octopus blood is copper-rich, making it exceptionally viscous, and as a result it requires a significant amount of pressure to pump blood through its body. According to A-Z Animals, splitting the workload across three separate pumps takes pressure off the main heart and keeps enough oxygen flowing to the gills.
That extra circulatory power supports an animal built almost entirely around predatory instincts in wildlife. Octopuses ambush crabs and mollusks with speed that a single-heart body plan likely could not sustain, and their keen vision helps them track prey in low light; see this guide on animals with big eyes for how their eyesight compares to other species. Some octopus species are also known to display cannibalism in animals during mating season, with females occasionally consuming smaller males after reproduction, a stark example of nature’s harsh realities in the cephalopod world.
2. Squid
Squid share the exact same three-heart layout as their octopus cousins, and it is not a coincidence. A common study species, the European squid (Loligo vulgaris), illustrates the pattern well: this three-heart design is the standard blueprint for the whole group of advanced cephalopods, the coleoids, which includes the giant Pacific octopus, meaning squid and cuttlefish are built the same way.
Two branchial hearts sit at the base of the gills and pump deoxygenated blood into them, and the newly oxygenated blood returns to a single systemic heart, which sends it out to the body. This arrangement, confirmed by anatomical studies published in WorldAtlas, lets squid sustain the rapid bursts of speed they rely on when hunting fish schools or escaping predators.
Squid rank among the ocean’s most efficient hunters, and their predatory instincts in wildlife depend heavily on that triple-pump circulation. Fast-twitch muscle needs a steady oxygen supply, and a sluggish single heart would leave a squid gasping mid-chase. If you want to explore more species that share squid’s first letter, check out this list of animals that start with S.
3. Cuttlefish
The common cuttlefish (Sepia officinalis) rounds out the three-hearted cephalopod trio, though its circulatory plumbing sets it apart from most other mollusks. Unlike most mollusks, cuttlefish possess a closed circulatory system, and like squids and octopuses, cuttlefish have three hearts.
Their hearts operate similarly to their fellow cephalopods, according to reporting from Yahoo News, with one systemic heart and two branchial hearts dividing the circulatory workload. A closed system means blood stays inside vessels rather than pooling freely in body cavities, which gives cuttlefish tighter control over blood pressure during their famous rapid color changes.
That control matters because cuttlefish shift pigment cells almost instantly to communicate, camouflage, or startle predators. Three hearts moving oxygen efficiently through a closed system helps power those muscle contractions without lag.
Key Insight: All three cephalopods on this list, octopus, squid, and cuttlefish, share the identical three-heart layout because they all belong to the coleoid group. The design is not a quirk of any single species; it is the standard cephalopod body plan.
4. Earthworm
The common earthworm (Lumbricus terrestris) is usually credited with five hearts in casual trivia, but the real anatomy is more nuanced. Worms are unusual in that they have five structures called aortic arches acting as basic hearts, rather than five separate heart organs in the way most people imagine.
These aortic arches are muscular, pulsing vessels that loop around the worm’s digestive tract near its head, squeezing blood forward into a single main blood vessel that runs the length of its body. The system works well enough for an animal with no lungs and no true heart chamber, moving oxygen-carrying hemoglobin dissolved directly in the plasma.
Important Note: Earthworms are frequently listed as having “five hearts,” but many anatomists argue they have no true heart at all, only five pulsing vessels that perform a heart’s job. Either description is defensible depending on how strictly you define a heart.
Earthworms also illustrate that multiple pumping structures are not the only alternative to a single heart. Some invertebrates skip pumping organs altogether; the animals with no heart guide covers several species, like jellyfish and starfish, that circulate fluid using body movement instead of any heart-like structure.
5. Hagfish
The hagfish (Myxine glutinosa) holds one of the more debated heart counts on this list. A letter published in The Lancet states plainly that the hagfish has five hearts.
Other anatomical breakdowns describe the same animal differently, counting one true systemic heart supported by several accessory pumps rather than five independent organs. The confusion is understandable given the hagfish’s unusual physiology: it has no jaw, no true spine, and the ability to tie its own body into a knot to escape predators or pry food loose.
Important Note: Sources disagree on whether the hagfish has three, four, or five hearts, depending on whether accessory pumps and portal hearts get counted separately or grouped with the main systemic heart. There is no single universally agreed-upon number.
What is not disputed is that hagfish blood pressure is remarkably low compared to most vertebrates, which is exactly why multiple pumps spread across the body make sense: a hagfish can survive for hours with almost no circulation at all, a survival trait researchers continue to study for insights into human cardiac disease.
6. Cockroach
The American cockroach (Periplaneta americana) is often cited as having thirteen hearts, but that popular claim does not hold up to scrutiny. A cockroach has one heart, and that heart has thirteen chambers arranged in a line.
Common Mistake: The thirteen-chamber heart gets misreported as thirteen separate hearts almost as often as the earthworm gets credited with five, according to WorldAtlas. One organ with many chambers is not the same as many organs.
Each chamber pulls in blood through tiny paired openings and passes it forward to the next, giving the insect a tube-shaped heart that functions almost like a conveyor belt. This segmented design suits an elongated insect body far better than a single compact chamber would.
Cockroaches are also a textbook example of animal survival behaviors under stress. When food runs short or population density climbs, some cockroach colonies turn to cannibalism in animals, consuming injured or dead members of their own species rather than let the nutrients go to waste. It is a grim but effective illustration of why animals eat each other when survival is on the line. Their resilience as a species also connects to their physiology more broadly; readers curious about other insects can browse animals with wings for comparison.
7. Horseshoe Crab
The Atlantic horseshoe crab (Limulus polyphemus) is often grouped into “multiple hearts” lists, though its real anatomy tells a different story. The horseshoe crab’s heart is a long tube that lies along the opposite side of the body from the nerve cord and extends almost the entire length of its body. That is a single heart, just an unusually long and structurally complex one.
What makes it stand out is the sheer number of openings feeding that one heart. It has eight pairs of slit-like openings, called ostia, through which blood enters from the pericardial chamber, and the blood is then pumped forward and escapes through three pairs of aortae, one pair of cerebral arteries, and a frontal artery, according to anatomical documentation from horseshoecrab.org.
Horseshoe crabs run an open circulatory system, meaning blood bathes tissues directly rather than staying confined to vessels, a setup shared with many arthropods. Their blue, copper-based blood has become critical to modern medicine because of its extreme sensitivity to bacterial toxins. These living fossils, whose pedipalps function almost like small claws for handling food, are a strong example of long-term animal survival behaviors; their body plan has barely changed in roughly 450 million years. See how their grasping limbs compare to other species with the animals with claws guide.
8. Leech
The medicinal leech (Hirudo medicinalis) belongs to the same phylum as the earthworm, Annelida, and its circulatory system follows a broadly similar logic: segmented, muscular vessels that contract to push fluid through the body rather than a single centralized pump.
Rather than a textbook heart, leeches rely on rhythmically pulsing blood vessels distributed along their segmented bodies. These contractile vessels move hemolymph, the leech’s circulatory fluid, through a mostly closed system that supports their highly specialized feeding behavior.
Leeches are predatory and parasitic in roughly equal measure, a vivid illustration of nature’s harsh realities. Many species latch onto a host, inject an anticoagulant to keep blood flowing, and feed for extended periods before detaching, a predatory instinct in wildlife that has made leeches useful in modern reconstructive surgery for restoring blood flow to reattached tissue. Their jaw structure, lined with small tooth-like ridges for piercing skin, is detailed further in this guide to animals with fangs.
9. Oyster
The Eastern oyster (Crassostrea virginica) rounds out this list with one of the more overlooked multi-heart arrangements. Research on oyster heart rhythm describes a main heart with three chambers, where two auricles receive blood from the gills and send it, about half a second later, to the ventricle, according to a study published on arxiv.org.
Beyond that main three-chambered heart, oysters carry backup pumps entirely separate from it. Two accessory hearts beat a couple of times per minute, independently from the principal heart, a detail also noted in an older anatomical report published in The Lancet describing accessory hearts that measurably expand and contract with each beat.
Oysters run an open circulatory system, so blood moves through tissue spaces as well as vessels, and their heart rate responds directly to water temperature, oxygen levels, and salinity. Because oysters filter enormous volumes of water daily, that extra circulatory capacity likely helps support the metabolic demands of constant filter-feeding, another organ working overtime much like the extra digestive chambers found in animals with multiple stomachs.
What These Nine Animals Have in Common
Lining these nine species up side by side shows just how differently “multiple hearts” can be interpreted across the animal kingdom. Some, like the cephalopods, have three genuinely separate heart organs. Others, like the cockroach and horseshoe crab, have one heart doing the work of many through extra chambers or openings.
| Animal | Heart Count | Blood Color | Circulatory System |
|---|---|---|---|
| Octopus | 3 (1 systemic, 2 branchial) | Blue | Closed |
| Squid | 3 (1 systemic, 2 branchial) | Blue | Closed |
| Cuttlefish | 3 (1 systemic, 2 branchial) | Blue | Closed |
| Earthworm | 0 true hearts (5 aortic arches) | Red | Closed |
| Hagfish | 3 to 5, depending on classification | Red | Closed |
| Cockroach | 1 heart, 13 chambers | Clear/yellowish | Open |
| Horseshoe Crab | 1 long tubular heart | Blue | Open |
| Leech | Pulsing vessels, no central heart | Red | Mostly closed |
| Oyster | 1 main heart (3 chambers) + 2 accessory | Colorless | Open |
Blood chemistry explains much of this variety. Copper-based hemocyanin, used by octopuses, squid, cuttlefish, and horseshoe crabs, carries oxygen less efficiently than iron-based hemoglobin and tends to be thicker, which pushes these animals toward extra pumping power. Body shape plays a role too: long, segmented animals like earthworms and leeches evolved distributed pumping structures rather than one centralized organ, simply because a single heart would struggle to move fluid efficiently across their entire length.
None of these adaptations exist for novelty. Each extra heart, chamber, or pulsing vessel solves a specific circulatory problem tied to that animal’s size, blood type, or lifestyle, whether that means fueling the burst-speed predatory instincts in wildlife seen in cephalopods or keeping a 450-million-year-old body plan alive through an open circulatory system. The animal kingdom did not settle on one heart because one heart does not always fit the job.