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Why do cephalopods have three hearts?

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A blue-ringed octopus with bright blue rings on its beige body crawls over a rocky, coral-strewn seabed. — cephalopod Blue-ringed octopus (genus *Hapalochlaena*).

Cephalopods possess three hearts to support their active, high-metabolic lifestyle and their closed circulatory system.12

The system consists of one main systemic heart and two branchial hearts. The two branchial hearts are located at the base of each gill; their primary function is to pump deoxygenated blood through the gill capillaries, where gas exchange occurs. Once the blood is oxygenated, it returns to the systemic heart, which then pumps the oxygen-rich blood throughout the rest of the body.231

This specialized arrangement is necessary because cephalopods rely on hemocyanin to transport oxygen, and the additional hearts ensure efficient circulation and pressure to meet the high energy demands of these animals.123