Quick Answer: The best-known animal with three hearts is the octopus. It has two branchial hearts that pump blood through the gills and one systemic heart that pumps oxygenated blood to the rest of the body. Squid and cuttlefish use the same three-heart plan because they are also cephalopods.
What Animal Has 3 Hearts?
An octopus has three hearts. This is one of the most unusual circulatory systems among familiar animals, but it makes sense when you look at how a cephalopod moves oxygen through its body.
| Heart | Number | Main job |
|---|---|---|
| Branchial heart | 2 | Pumps oxygen-poor blood toward the gills |
| Systemic heart | 1 | Pumps oxygen-rich blood from the gills to the body |
| Total | 3 | Maintains circulation through gills and body |
The two branchial hearts sit near the gills. After blood passes through the gills and picks up oxygen, the systemic heart sends that oxygenated blood to the arms, organs, nervous system, and other tissues.
Why Does an Octopus Need Three Hearts?
Octopuses are active marine animals with a closed circulatory system. Their blood uses hemocyanin, a copper-containing oxygen-transport protein, rather than the iron-containing hemoglobin that makes human blood red.
The separate branchial hearts help push blood through the gills, while the systemic heart maintains circulation through the body. This arrangement gives cephalopods a powerful way to keep oxygen moving through tissues despite the resistance involved in pumping blood through the gills.
It is better to describe the three-heart system as a specialized cephalopod circulation design than to say that octopuses simply “need extra hearts because the ocean has less oxygen.” Octopus species live in many different marine environments, and the cardiovascular system is part of a much broader evolutionary adaptation.
How Do the Three Octopus Hearts Work?
The Two Branchial Hearts
Each branchial heart is associated with one gill. These hearts receive oxygen-poor blood returning from the body and pump it through the gill, where gas exchange occurs.
The Systemic Heart
The systemic heart receives oxygenated blood after it leaves the gills and pumps it through the main arteries to the rest of the body.
The basic route can be simplified as:
Body → branchial hearts → gills → systemic heart → body
Does an Octopus Heart Stop When It Swims?
Popular summaries often say that the systemic heart “stops beating when an octopus swims.” There is physiological evidence that systemic-heart activity can be strongly suppressed or interrupted during jet-swimming and powerful mantle contractions.
The important takeaway is that jet swimming is energetically demanding for octopuses, and crawling along the seafloor is often a more efficient way for them to move. The statement should not be interpreted as meaning that an octopus remains without body circulation for long periods every time it moves through the water.
Why Is Octopus Blood Blue?
Octopus blood appears blue when oxygenated because it contains hemocyanin. Hemocyanin uses copper at its oxygen-binding sites. When oxygen binds to the copper-containing protein, the oxygenated form appears blue.
Humans and other vertebrates usually rely on hemoglobin, which contains iron and makes oxygenated blood look red.
| Feature | Octopus | Human |
|---|---|---|
| Oxygen-carrying protein | Hemocyanin | Hemoglobin |
| Metal involved | Copper | Iron |
| Oxygenated color | Blue | Red |
| Number of hearts | 3 | 1 |
For more examples, see Which Animals Have Blue Blood?.
Do Squid Have Three Hearts?
Yes. Squid also have two branchial hearts and one systemic heart. Their circulatory system follows the same general cephalopod pattern as the octopus.
Squid are often much more active open-water swimmers than octopuses, but both groups rely on a closed circulatory system and hemocyanin-based oxygen transport.
Do Cuttlefish Have Three Hearts?
Yes. Cuttlefish also have three hearts: two branchial hearts associated with the gills and one systemic heart supplying the rest of the body.
This means the three-heart arrangement is not unique to octopuses. It is characteristic of the advanced cephalopod groups that include octopuses, squid, and cuttlefish.
Are Octopuses the Only Animals With Multiple Hearts?
No. Several animals have unusual pumping structures, but the terminology can be misleading.
| Animal | Circulatory pumps | Important distinction |
|---|---|---|
| Octopus | 3 true hearts | 2 branchial + 1 systemic |
| Squid | 3 true hearts | Same basic cephalopod pattern |
| Cuttlefish | 3 true hearts | Same basic cephalopod pattern |
| Hagfish | 1 main heart + accessory pumps | Often oversimplified online as “four hearts” |
| Earthworm | Aortic arches | These are pumping vessels, not vertebrate-style hearts |
Does a Hagfish Really Have Four Hearts?
Hagfish are often described online as having “four hearts,” but that wording is oversimplified. They have a main systemic heart plus accessory pumping structures that help move blood through different parts of the body.
So if the question is “what familiar animal has exactly three true hearts?”, the clearest answers are octopuses, squid, and cuttlefish.
Do Earthworms Have Five Hearts?
Not in the same anatomical sense as an octopus or a human. Earthworms have several pairs of muscular aortic arches that help pump blood through their closed circulatory system. These are often nicknamed “hearts,” but biologically they are specialized blood vessels rather than separate chambered hearts.
Do Octopuses Have Three Brains Too?
No. The common phrase that an octopus has “nine brains” is a simplification. An octopus has one central brain plus large clusters of neurons in its arms. Much of its nervous system is distributed outside the central brain, allowing the arms to process substantial sensory and motor information locally.
That distributed nervous system is remarkable, but it does not mean the animal literally has nine independent brains.
How Many Hearts Does an Octopus Have Compared With Other Animals?
| Animal | Heart count / main pumps |
|---|---|
| Human | 1 heart |
| Dog | 1 heart |
| Fish | 1 main heart |
| Octopus | 3 hearts |
| Squid | 3 hearts |
| Cuttlefish | 3 hearts |
| Earthworm | Multiple aortic arches, not true separate hearts |
FAQ
What animal has three hearts?
Octopuses, squid, and cuttlefish have three hearts.
Why does an octopus have 3 hearts?
Two branchial hearts pump blood through the gills, while one systemic heart pumps oxygenated blood to the rest of the body.
Which heart pumps blood to an octopus's body?
The systemic heart pumps oxygenated blood from the gills to the organs and tissues.
Which hearts pump blood to the gills?
The two branchial hearts pump oxygen-poor blood through the gills.
Does an octopus have blue blood?
Yes. Oxygenated octopus blood appears blue because its oxygen-carrying protein, hemocyanin, contains copper.
Do squid have 3 hearts?
Yes. Squid have two branchial hearts and one systemic heart.
Do cuttlefish have 3 hearts?
Yes. Cuttlefish share the same basic three-heart cephalopod circulatory plan.
Do earthworms really have 5 hearts?
Not true hearts in the same sense. Earthworms have multiple muscular aortic arches that act as blood-pumping vessels.
Which animal has 4 hearts?
Hagfish are sometimes described as having four hearts, but a more accurate description is one main heart plus several accessory blood pumps.
Final Answer
The octopus is the classic animal with three hearts. Two branchial hearts pump blood through its two gills, and one systemic heart distributes oxygenated blood throughout the body. Squid and cuttlefish also have three hearts, making this one of the defining circulatory features of these advanced cephalopods.
