Quick answer
An octopus has three hearts. Two 'branchial' hearts pump blood through the gills to pick up oxygen, and one larger 'systemic' heart pushes that oxygenated blood around the rest of the body. Their blood is blue because it uses copper-based haemocyanin instead of iron-based haemoglobin to carry oxygen.
Octopus hearts and blood at a glance
| Number of hearts | Three |
| Branchial (gill) hearts | Two — pump blood through the gills |
| Systemic heart | One — pumps blood to the body |
| Blood colour | Blue |
| Oxygen carrier | Haemocyanin (copper-based) |
| Swimming quirk | Systemic heart stops when swimming, so they prefer to crawl |
Why an octopus needs three hearts
The three-heart arrangement is a neat engineering solution to the octopus's body plan. Two smaller branchial hearts sit beside the gills, and their only job is to push blood through the gill tissue so it can absorb oxygen from the water. The third and largest heart, the systemic heart, then takes that freshly oxygenated blood and pumps it out to the muscles, organs, and the rest of the body.
This division of labour matters because octopus blood does not carry oxygen as efficiently as our own. Splitting the circulation — one stage dedicated entirely to loading oxygen at the gills, another to delivering it — helps the system keep up with the demands of an active, intelligent predator.
Why octopus blood is blue
Human blood is red because it carries oxygen on haemoglobin, a protein built around iron. Octopuses, along with many other molluscs and some arthropods, use haemocyanin instead — a protein built around copper. When haemocyanin binds oxygen, it turns the blood blue rather than red.
Haemocyanin works especially well in the cold, low-oxygen conditions of the deep sea, which is one reason it has persisted in octopuses. The trade-off is that it is less efficient than haemoglobin at carrying oxygen overall, which is part of why the octopus needs its multi-heart system to move blood quickly enough.
The strange reason octopuses prefer crawling
There is a quirky consequence to all this plumbing. When an octopus swims by jetting water, the systemic heart actually stops beating. Swimming is therefore tiring and slightly stressful for the animal, because its main pump is briefly offline and oxygen delivery dips.
That is why octopuses, despite being able to jet away quickly when threatened, usually prefer to crawl across the seabed using their arms. Crawling lets all three hearts keep working steadily, making it the more comfortable and energy-efficient way for one of the ocean's cleverest animals to get around.
Octopus hearts: FAQs
How many hearts does an octopus have?
An octopus has three hearts: two branchial hearts that pump blood through the gills to collect oxygen, and one systemic heart that pumps the oxygenated blood to the rest of the body.
Why does an octopus have three hearts?
The two gill hearts push blood through the gills to absorb oxygen, while the larger systemic heart delivers that oxygen-rich blood around the body. The split helps compensate for octopus blood carrying oxygen less efficiently than human blood.
Why is octopus blood blue?
Octopus blood is blue because it uses haemocyanin, a copper-based oxygen-carrying protein, instead of the iron-based haemoglobin in human blood. Copper turns the blood blue when it binds oxygen.
Does an octopus heart stop when it swims?
Yes. The systemic heart stops beating when an octopus swims by jetting, which makes swimming tiring. This is why octopuses usually prefer to crawl along the seabed instead.
Do all octopuses have three hearts?
Yes, three hearts and blue, copper-based blood are standard across octopus species. The same basic circulatory design is shared with many other cephalopods such as squid and cuttlefish.
How many brains does an octopus have?
An octopus has one central brain plus a cluster of nerve cells in each of its eight arms, so it is often said to have nine 'brains'. Each arm can process information and act with a degree of independence.