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Animals With Two Or More Hearts? Here’s 10 Unique Animals

Nature is full of many different animals, each amazing in its own unique way. Some can fly, some can breathe underwater, some can see at night, some can regrow limbs, the uniqueness goes on and on. Believe it or not, scientists have even found several different animals with more than one heart.

With different amounts ranging from two to thirteen. Continue reading below to see which is your favorite animal with two hearts.

1. Trout

Believe it or not, the trout actually has two hearts. Not only is it an animal with two hearts, but the trout is also the only animal to naturally have two hearts. The first heart functions as the normal blood-pumping organ and like in most fish, it is right behind the throat, the second heart is what is known as a caudal heart.

Brown Trout
Brown Trout

This caudal heart is found near the last vertebrae on the trout’s backbone. The caudal heart’s job is to collect blood from the tail and force it into higher-pressure caudal veins where it will more efficiently flow back to the heart.

An interesting thing about the caudal heart is that it is believed to only be active when the trout are swimming. This suggests to researchers that it is used when the trout is active and needs more oxygen.

2. Hagfish

The hagfish is an eel-shaped marine fish. Commonly, the hagfish is most famous for its ability to produce a gross amount of slime, on average it can produce 400 times its volume worth of slime. The Pacific Hagfish specifically can produce 24 liters.


The slime is used as a defense mechanism and is designed to clog up the gills of other fish that are threatening it, nature is fascinating. But another fun fact about the hagfish is that they have four hearts.

Because they live on the ocean floor, where there is not much oxygen in the water, they need four hearts in order to live, in fact, the hagfish’s hearts will continue to beat for over a day without oxygen, keeping them alive.

The first of the hagfish’s four hearts is what is known as a branchial heart, which means that its job is to pump blood to the entire body. Meanwhile, the other three hearts are auxiliary.

Expert Tip: The job of these other three hearts is to act as accessory pumps helping the main heart oxygenate the blood and then pump that blood throughout the body of the hagfish.

3. Cuttlefish

Cuttlefish is an invertebrate and marine mollusks species that mainly live in shallow waters. Cuttlefish are found in the wild across the world. With the largest species of cuttlefish being native to the waters of Australia.


Although most cephalopods such as octopuses and squids are considered to be rather intelligent, it is the cuttlefish that might just be the smartest of the bunch. As a matter of fact, the cuttlefish is considered by most researchers to be the most intelligent out of all the invertebrates.

The cuttlefish, as a species, is genetically a close relative to the squid and the octopus who are two other animals that have multiple hearts. However, unlike its genetic cousin, the cuttlefish only has three hearts. The job of the first heart is to pump oxygenated blood throughout the body.

The other two hearts are branchial, Branchial hearts are accessory pumps that are there to help the main heart pump blood in the body of a cephalopod like a cuttlefish. In a cuttlefish, the job of the two branchial hearts is to pump blood specifically to the cuttlefish’s gills, there is one heart for each gill.

4. Earthworms

The common earthworm is a terrestrial invertebrate. They serve a crucial role in nature as they help to improve the quality of the soil they are living in which then makes the plants growing in that soil grow healthier and stronger. Earthworms are among the most common animals that have more than one heart.


These creatures can be discovered pretty much everywhere and anywhere, provided that there is some dirt that they can live in. What makes earthworms truly interesting is that they have five hearts, even though they are very simple and primitive organs. Instead of the standard heart, what the earthworm does have is five “pseudo-hearts”.

The “pseudo-hearts” are essentially five pairs of aortic arches that work in a similar way to how a heart works. The five arches in the earthworm, which are each made of only one chamber, can be found near the mouth of the earthworm.

Expert Tip: Earthworms, as a species, don’t breathe through mouths but through their skin. They rely on moisture to help make their respiratory system work.

Once the oxygen has made its way into the earthworm’s body, one of the aortic arches will act as a primary organ and will pump the oxygenated blood to the rest of the arches and throughout the body. The earthworm’s nerve cells are used to regulate a heartbeat.

5. Squids

Squid are cephalopods that have elongated bodies, big eyes, eight arms, and two long tentacles. Like all the other cephalopods in the ocean, the squid has a very distinctive head, a bilateral symmetry, and a mantle (which is the scientific term for a squid’s body).

Squids are mainly soft-bodied but do have an internal skeleton that is in the shape of a rod, made of a substance called chitin. Different kinds of squids can naturally be found in every ocean on earth, and most species of squids are rather small. However, some of them can grow to be an extremely large size.


The infamous giant squid is among the biggest creatures on earth and is likely to be the largest animal with more than one heart. Squids come in a variety of different species that can widely vary in size, but all of the different species have three hearts. The three hearts serve the same function across all the different species.

There is the one main heart whose job is to pump oxygenated blood throughout the squid’s entire body. They also have two branchial hearts whose job is to pump blood through the squid’s gills to its main heart to then be oxygenated.

6. Octopus

The octopus is an aquatic soft-bodied, eight-limbed mollusk that belongs to the order of Octopoda. The order of Octopoda contains about 300 different species and itself is classified within the class of Cephalopoda, along with such creatures as squids and cuttlefish.


Octopuses can be found living in almost any ocean on earth and at just about any depth. Different kinds of octopuses can be found living in both the deep abyss of the ocean and on the shores of the ocean. The octopus has the incredible ability to alter its shape and color.

Expert Tip: There are also some researchers who have observed evidence that the octopus is a very intelligent species that in some cases can learn how to use tools.

Much like their genetic cousin the squid, octopuses exist in hundreds of different species that come in a wide variety of sizes, but all of them have three hearts.

The three hearts serve the same function across all the different species. There is the one main heart whose job is to pump oxygenated blood throughout the octopus’ entire body. They also have two branchial hearts whose job is to pump blood through the octopus’ gills to its main heart to then be oxygenated.

7. Cockroaches

Cockroaches are a type of insect that belongs to the order Blattodea which also includes another famous pest, the termites. There are thousands of unique types of cockroaches. Cockroaches can live everywhere, but they are typically known as pests that live in man-made buildings.


The cockroaches’ ability to famously survive in different harsh conditions and with injuries that would kill any other creature is well documented. One reason why they are so difficult to kill is that they actually have 13 hearts.

Well, technically, scientists are now saying that cockroaches have just one heart, with 13 chambers, but practically speaking they might as well have 13 individual hearts. The chambers are in a sequence, with each chamber pumping blood over to the next one in the line.

This strange setup in their body is what makes them so hard to kill since it is almost impossible for a cockroach’s heart to fail. This is because a cockroach’s heart won’t stop beating even if one of its chambers malfunctions. Although the heart will start working less effectively, it just won’t kill the cockroach, like it might any other living creature.

Scientists even have taken the design of the cockroaches’ hearts and studied them to help develop effective artificial organs.

8. Barosaurus

Now, this creature is not scientifically proven to have had more than one heart and there is still some debate in the scientific community about it. but it is still worth discussing. The Barosaurus was a ginormous, long-tailed, long-necked, and plant-eating dinosaur that walked the earth about 200 million years ago.


Because it was so big it may have had as many eight hearts to be able to pump blood up to its very high up head, or at least that is what some paleontologists theorize.

Some scientists disagree about whether or not the Barosaurus, which stood at about 45 feet tall, normally stood like a giraffe and ate from the treetops or if it kept its neck more parallel to the ground in order to feed. However, other scientists argue that the shape of the Barosaurus’ vertebrae suggests that the former is true.

This was discovered when a Barosaurus skeleton was reconstructed at New York’s American Museum of Natural History. If this was in fact true, then Barosaurus would have to have an extremely strong cardiovascular system in order to pump blood all the way from its chest to its very high up head.

Some scientists theorize that the Barosaurus might have had a heart in its thorax, in the base of its neck, and then three pairs of hearts up its 36-foot-long neck in intervals. Again, these are all just theories, and we may never truly know the biology of some dinosaurs.

9. Horse

Everyone knows what a horse is, they are the majestic animal that humans have been riding and breeding for centuries. Surprisingly, even horses have more than one heart, well they are sort of doing. At the very bottom of each horse’s feet is a very special organ that is referred to as a frog.


While not exactly a heart, the frog will act as a sort of blood reservoir in the horse. Every time the horse places its foot on the ground, the blood that is in the frog will be pumped out of and away from the frog and will go into the arteries of the horse.

Expert Tip: While to some people the frogs may not be a heart, the sole purpose of the frogs is to pump blood around the body of the horse.

Which is exactly the same function that a heart performs. Therefore it is debatable that a horse has five hearts.

10. Humans

Again, just like with horses, it is debatable that humans belong in this category of animals with more than one heart. Obviously, most humans have just one heart, which is not up for debate. However, not every human has only one heart beating in their chest.

Not every human has only one heart beating in their chest
Not every human has only one heart beating in their chest

In some rare cases, in a medical emergency when someone has a heart defect and gets heart surgery, the doctors will not actually remove the old heart and replace it with a new one. Instead, what they do, if the old heart is at least somewhat functioning, is graft a new heart onto the hold heart.

The new heart helps the old heart pump blood throughout the body. So, technically speaking, there are humans walking around with two hearts in their chests.


There are quite a few creatures that have multiple hearts beating in their bodies on this planet. Some very clearly have more than one heart, like the squids and octopuses. Some technically have multiple hearts like the earthworm.

Some might have had more than one heart, like the Barosaurus and some debatably have more than one heart, like horses and humans.

All in all, whether it is an animal with two hearts or thirteen, this diversity is just one thing that makes nature so fascinating.

If you have any questions please ask them below.

About Rencel Leyran