Octopuses have three hearts: two branchial hearts and one central heart. The branchial hearts are located near their gills and the central heart is located at the back of their mantles. The branchial hearts pump blood through their gills and the central pumps blood to the body.
Octopuses are one of the most fascinating creatures in the ocean. Their silhouette is instantly recognizable and many marine life lovers are fascinated by these eight-legged animals.
But as famous as they are, there are many mysteries about them and their anatomy. Questions regarding octopus hearts are especially common:
- How many hearts do octopuses have?
- What do octopus hearts look like?
- How do octopus hearts work?
This article uncovers the facts and workings of octopuses’ hearts, including their location, function, and types.
How Many Hearts Do Octopuses Have?
Octopuses have three hearts: two near their gills and one at the back of their mantle. Their main function is to circulate blood in the octopus’ body.
A uniqueness of cephalopods (“cephalo” referring to head, “pod” referring to feet), including octopuses, is their closed circulatory system. This means that their blood is transported in a closed system of blood vessels (humans also have a closed circulatory system).
All other mollusks have open circulation systems, meaning their organs are submerged in blood inside their body.[1]
The three hearts of the octopus pumps blood through blood vessels. This makes blood travel farther, in larger quantities, and more efficiently.
Types of Octopus Hearts
Octopuses have two types of hearts: the branchial heart and the central heart. The two types of hearts have the similar function of pumping blood. The main difference is where they pump it and the location of the hearts.
1. Branchial Hearts
The branchial hearts, or gill hearts, are located next to the gills. They pump blood through the gills to oxygenate them. The oxygenated blood then gets pumped into the central heart.
Here are the function and characteristics of the branchial hearts:
- Their main function is to get blood oxygenated.
- They beat simultaneously.
- They receive used blood through the anterior and lateral vena cavae (or vena cava cephalica).
- They pump blood into the afferent branchial vessels in the gills.
- The blood pumped by them goes to the central heart.
2. Central Heart
Octopuses have one central heart, also called systemic heart or main ventricle. It is located between the two branchial hearts and further back in the mantle. It pumps oxygenated blood to the body.
Here are the functions and characteristics of the central heart:
- Its main function is to distribute oxygenated blood in the body.
- It stops beating when the octopus swims.
- It receives blood through the afferent branchial vessels.
- It pumps blood through the main cephalic artery.
What Do Octopus Hearts Look Like?
Octopus hearts are blueish and small, but there isn’t an exact answer to what they look like. The 300 species of octopuses have vastly different hearts.
Most illustrations of octopus hearts show them as oval organs, no bigger than the eyes.[2]
| Characteristic | Branchial Hearts | Central Heart |
| Size | 0.5-1 in | 0.5-1 in |
| Shape | Oval, elongated | Oval |
| Color | Blue | Blue |
| Location | Near the gills inside the mantle | Further back and central inside the mantle |
Size
Octopus hearts are 0.5-1 in in length, about the same size as the diameter of their eyes.[3]
Although octopus hearts are relatively small compared to their bodies, they greatly range in size. The largest giant Pacific octopus is about 14 feet while the minute Octopus wolfi is less than an inch. Naturally, a giant Pacific octopus has proportionally bigger hearts than an Octopus wolfi (an Octopus wolfi is smaller than a giant Pacific octopus heart).[4]
Shape
Octopus hearts are oval. Branchial hearts are enlarged portions of a vein and slightly elongated compared to central octopus hearts.[5]
Color
Octopus hearts are blue because they have blue blood.[6] If octopuses didn’t have blood, the color of their heart would be the same color as their meat: milky-white.
Location
Branchial hearts are located next to the gills on both sides of the octopus’ mantle.
The central heart is located above the kidney. It is close to the branchial hearts but further back.[7]
Why Do Octopuses Have Three Hearts?
Octopuses have three hearts for increased blood flow. Their blood transports oxygen with hemocyanin which is a poor oxygen carrier. They need three hearts to efficiently maintain their oxygen capacity.
Octopuses need their hearts to pump blood and distribute oxygen, like all other animals. To do this, the blood needs an oxygen carrier.
The most common oxygen carrier is hemoglobin, but octopus blood contains hemocyanin instead. Hemocyanin carries oxygen inefficiently, so octopuses developed multiple hearts to compensate.
Their three hearts essentially help to distribute blood evenly throughout their bodies.
Octopuses have three hearts for the following reasons:
- To distribute oxygen
- To compensate for the poor oxygen carrying capacity of hemocyanin
- Branchial hearts: to pump blood through the gills
- Central heart: to circulate oxygenated blood through the body
What Happens if One of The Hearts Stops Working?
If one of the octopus’ hearts stops working, it may survive. It depends on what heart it is.
If one of the branchial hearts fails, the octopus does not die. Octopuses can breathe through their skin, allowing them to survive without one of their branchial hearts functioning. They can also breathe on land for short periods.[8]
If both branchial hearts or the central heart fail, octopuses die. Although they can breathe through the skin, octopuses can’t get enough oxygen to support the entire body. The central heart is crucial: if it stops working, the organs of the octopus don’t receive any oxygen and will start failing.
The central heart does stop when they swim, but octopuses tire quickly. This is why they crawl on the seafloor.
How Do Octopus Hearts Work?
Octopus hearts contract periodically to pump blood. The branchial hearts pump blood through the gills and into the central heart. The central heart then oxygenates the blood and pumps it through the main cephalic artery into the body. The used blood drains into the branchial hearts through the vena cava cephalica, repeating the cycle.
The hearts circulate blood to distribute oxygen. The process starts at the gills.
As the octopus breathes in, the blood in the gills gets oxygenated. The branchial hearts pump the oxygenated blood to the central heart, which sends it out through the vessels to the body.
After the oxygen is distributed, the blood returns to the branchial heart so the process can start all over again.
A full circulation involves all three hearts and takes the following steps:
- Blood in the gill’s vessels (afferent branchial vessels) gets oxygenated.
- Branchial hearts pump blood to the central heart.
- The central heart pumps blood through the main cephalic artery.
- Blood circulates and distributes oxygen.
- Used blood returns to the branchial hearts through the anterior and lateral vena cavae.
- Branchial hearts pump blood into the afferent branchial vessels.
- Repeat.
How Fast Do Octopus Hearts Beat?
Octopus hearts normally beat at a pace of 40-50 bpm.[9] The heartbeat is regulated by the cardiac ganglion, a cluster of nerves acting as a pacemaker. This function is found in all three hearts.
Octopus Hearts Compared to Human Hearts
Octopus hearts work similarly to human hearts, but instead of having one heart that does all of the work, the heart functions are split across three hearts. Human hearts are also bigger than octopus hearts and are located in the chest. Octopus hearts are blue and human hearts are red.
The hearts of humans and octopuses both have the same purpose: to pump blood and deliver oxygen to the body.
The main difference is that a human heart pumps blood through the lungs (right ventricle) and through the body (left ventricle) at the same time. Octopuses need three hearts for the same task: the bronchial hearts act as the right ventricle and the central heart as the left ventricle.
| Characteristic | Human Heart | Octopus Hearts |
| Number | 1 | 3 (2 branchial, 1 central) |
| Size | Length: 4.72 in, width: 3.34 in, thickness: 2.36 in[10] | 0.5-1 in |
| Shape | Like an “upside-down pear”[11] | Oval |
| Function | To pump blood through lungs, to pump oxygenated blood through the body | Branchial: pump blood through gills, Central: pump blood through the body |
| Location | Front of the chest, behind and left to the sternum | Both in the mantle, Branchial: next to the gills, Central: behind and between the branchial hearts |
Conclusion
Octopuses have three hearts in their mantles. The two branchial hearts are next to the gills and the central heart is between and behind them. They are oval, blue, and about an inch big.
Octopuses have three hearts to compensate for their blood’s poor oxygen-carrying capacity. The branchial hearts pump blood through the gills and into the central heart. The blood then gets pumped into the body and returns to the branchial heart.
FAQs
How Many Brains Does an Octopus Have?
Octopuses have nine brains. The main purpose of having nine brains is increased control of their arm movements. Their doughnut-shaped central brain is located in their head around the esophagus. The eight mini-brains essentially give a form of free will to each of the octopus’ tentacles.
Can Octopuses Have More Than Three Hearts?
No, octopuses cannot have more than three hearts. All cephalopods have three hearts: Two branchial and one systemic. These take care of the octopus’ circulatory needs sufficiently. The animals with the most hearts aren’t octopuses, however, as the hagfish has four hearts.
Why is Octopus Blood Blue?
Octopus blood is blue due to hemocyanin. It is a protein that carries oxygen in octopuses and contains copper. When O2 bonds with copper, it turns blue, which gives octopus blood its signature blue color.[12]
