why do octopus have three hearts at night?

The Deep Dive

An octopus's circulatory system is a marvel of evolutionary engineering, built to support its soft, boneless body and active predatory habits. The system is closed, meaning blood stays within vessels. The two branchial hearts are located at the base of each gill. Their sole job is to overcome the high resistance of the gill filaments, pushing deoxygenated blood through them to release carbon dioxide and absorb oxygen from the water. This oxygen-rich blood then flows into the systemic heart, a larger, more muscular pump. This third heart's job is to generate enough pressure to send the oxygenated blood through the aorta and throughout the entire body, fueling the octopus's muscles and complex nervous system. The systemic heart is so specialized that it actually stops beating when the octopus swims, which is why they prefer crawling; swimming exhausts them quickly as their body becomes starved of oxygenated blood.

Why It Matters

This three-heart system is a masterpiece of biological efficiency for a soft-bodied, high-energy predator. It allows the octopus to be a voracious hunter and a quick escape artist by ensuring its muscles receive a constant, high-volume supply of oxygen. Studying this unique cardiovascular design informs biomedical engineering and robotics, inspiring more efficient fluid pumps and soft robotic actuators. Furthermore, it highlights the diverse evolutionary solutions to the challenge of oxygen transport in aquatic environments, reminding us that complex life can evolve very different blueprints than our own.

Common Misconceptions

A common myth is that octopuses only have three hearts at night or that the hearts take turns working. In reality, the three hearts are always present and function continuously, though their output changes with activity. The branchial hearts beat constantly to oxygenate blood, while the systemic heart pulses to circulate it. Another misconception is that all three hearts are identical. In truth, they are structurally and functionally distinct: the two branchial hearts are auxiliary pumps for the gills, while the systemic heart is the main, high-pressure pump for the entire body.

Fun Facts

• An octopus's blood is blue because it uses a copper-based protein called hemocyanin to transport oxygen, which is more efficient in cold, low-oxygen environments than our iron-based hemoglobin.
• If an octopus's systemic heart stops for too long, it will die, which is why they are reluctant to swim for extended periods and prefer to crawl along the seafloor.