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The Three-Heart Circulatory System
Octopuses possess an unusual cardiovascular architecture built around three distinct hearts. Two smaller branchial hearts push blood through the gills to collect oxygen, while a larger systemic heart distributes oxygenated blood throughout the rest of the body. This division helps maintain adequate pressure to move blood across both the respiratory organs and body tissues.
Unlike mammals, octopuses rely on hemocyanin, a copper-based protein that turns their blood blue, to transport oxygen. Hemocyanin is generally less efficient at binding oxygen than iron-based hemoglobin, making high blood flow essential for keeping the animal energized.
Why Swimming Pauses the Main Heart
When an octopus swims using jet propulsion, it forcefully contracts its mantle to blast water out of its siphon. This powerful muscular contraction creates intense pressure inside the body cavity, which physically compresses the systemic heart and causes it to stop beating for the duration of the swim.
Because systemic blood flow halts during jet propulsion, swimming rapidly drains the creature of oxygen. Consequently, octopuses experience swift physical exhaustion when swimming, which is why they reserve jet propulsion primarily for sudden escapes rather than routine travel.
A Temporary Pause, Not a Fatal Event
A common misconception is that a heart stopping is always a fatal event for an octopus. In reality, this brief cardiac pause is a normal physiological response to the mechanical strain of fast swimming. As soon as the octopus settles back onto a surface and rests, its systemic heart resumes beating normally without causing permanent harm.
Quick facts
- An octopus relies on two branchial hearts for its gills and one systemic heart for the rest of its body.
- Copper-rich hemocyanin gives octopus blood its blue color and transports oxygen through the body.
- Crawling along the sea floor with their arms requires significantly less energy for octopuses than swimming.
- The main heart naturally resumes beating once an octopus stops swimming and begins to rest.
Frequently asked questions
Crawling allows the systemic heart to keep beating continuously, making it much less tiring than swimming. Octopuses generally save swimming for quick escapes from danger.
Octopus blood is blue because it uses a copper-based protein called hemocyanin to carry oxygen instead of iron-based hemoglobin.
No, the pause is a natural mechanical reaction to mantle contraction. The heart restarts as soon as the octopus stops jetting and resumes resting.
