Octopuses are among the most fascinating creatures in the ocean—not just because of their eight arms and exceptional intelligence, but because they have three hearts. This odd feature isn’t just a biological quirk—it plays a critical role in how they move, survive, and possibly even how they sleep.
The Three-Heart System
An octopus has one main heart called the systemic heart and two smaller ones called branchial hearts. The branchial hearts are located near the gills and are responsible for pumping blood through the gills where it gets oxygenated. From there, the oxygen-rich blood is sent to the systemic heart, which then circulates it through the rest of the body.
What’s even more interesting is that the systemic heart stops beating when the octopus swims. This means that while they’re actively swimming, the body isn’t being pumped with oxygenated blood efficiently. This might be one reason why octopuses prefer crawling along the ocean floor rather than swimming for long periods—it’s simply more sustainable for their hearts.
Implications for Sleep
While we’re still learning about octopus sleep, their unique circulatory system seems to play a role. Research shows that octopuses have two distinct sleep states: quiet sleep and active sleep, similar to REM in humans. During quiet sleep, their bodies are still, and colors fade. In active sleep, however, their skin pulses with changing colors, and their arms may twitch.
Scientists believe the active sleep phase may be when the octopus is dreaming. With three hearts, the octopus can maintain vital circulation even if one heart slows down during sleep. This redundancy could make complex sleep states—like dreaming—more stable, even in the deep sea.
A Window Into an Alien Intelligence
The octopus’s three-heart system isn’t just a cool fact—it highlights how different paths in evolution can produce intelligent, conscious behavior. While we rely on one heart and a brain enclosed in a skull, the octopus spreads its nervous system through its arms and balances three hearts in a carefully choreographed system.
Next time you spot an octopus in a nature documentary, remember: there’s a lot more going on beneath those tentacles than meets the eye—especially when it sleeps.