Octopuses have three hearts, and two of them stop beating when they swim.
The two smaller hearts pump blood to the gills, and the main heart pumps blood to the rest of the body. When an octopus swims, the main heart actually stops beating — which is why they prefer crawling along the ocean floor. Swimming literally exhausts them.
Bonus twist: their blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin to transport oxygen.
So yes — three hearts, blue blood, and they get tired of cardio.
Octopuses have three hearts—but that’s not the unusual part.
Two of their hearts stop beating entirely when they swim.
The two “branchial” hearts pump blood to the gills, and the main heart pumps it to the rest of the body. When an octopus swims, the main heart works so hard that the branchial hearts temporarily stop. That’s why octopuses prefer crawling over swimming—swimming literally exhausts their circulatory system.
As a bonus twist: their blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin to carry oxygen.
Octopuses have three hearts, and two of them stop beating when they swim.
That’s why octopuses prefer crawling to swimming—swimming is so physiologically taxing that it essentially shuts down two of their hearts, making it exhausting and inefficient. Over time, this is thought to be one reason most octopus species evolved to live on the seafloor rather than in open water.
Bonus twist: their blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin to transport oxygen.