Does an Octopus Have Three Hearts?
Dive beneath the waves to discover why an octopus needs three hearts and blue blood.
Read along
An octopus really does have three hearts. Two are called branchial hearts, and each one pumps blood toward a gill so the blood can collect oxygen from the water. The third, called the systemic heart, sends that oxygen-rich blood around the rest of the body. Octopus blood is blue because it uses a copper-containing protein called hemocyanin to carry oxygen. Hemocyanin works well in cold ocean water, although it is less efficient than the iron-containing hemoglobin that makes human blood red. When an octopus swims, its systemic heart temporarily stops beating, which makes swimming tiring. That is one reason octopuses often prefer to crawl along the seafloor using their flexible arms.
Inside the story
Scene by scene
Pause, look closer, and discover the science behind each part of the adventure.
Scene 0101
Three hearts under the sea
“Inside an octopus, three separate hearts keep blood moving through its unusual body.”
Two branchial hearts serve the gills, while one systemic heart supplies the organs and muscles throughout the body.
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Blood that looks blue
“Copper-rich hemocyanin carries oxygen and gives octopus blood a blue appearance.”
Human hemoglobin contains iron and looks red when oxygenated. Octopus hemocyanin contains copper and is well suited to cold, low-oxygen water.
Scene 0303
Crawling saves energy
“Because swimming is tiring, an octopus often glides and crawls across the ocean floor instead.”
The systemic heart pauses during jet-propelled swimming. Crawling can therefore use less energy and is often the octopus's preferred way to travel.
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