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Curious Facts / Nature

Do an Octopus’s Three Hearts Do the Same Job?

The number is only the beginning. Explore the different jobs of an octopus’s three hearts.

Two hearts send blood to the gills; one sends it around the body

A schematic of the blood route, not the positions of organs. Numbers count hearts; they do not show proportions of blood or body size.

  1. Oxygen-poor blood

    Travels towards the gills

  2. Branchial heart · 1

    Pumps blood to a gill

    Branchial heart · 1

    Pumps blood to a gill

  3. Gill

    Blood gains oxygen from water

    Gill

    Blood gains oxygen from water

  4. Systemic heart · 1

    Pumps blood that has gained oxygen

  5. Around the body

    One connected circulation

Visual evidence: Smithsonian Ocean — Cephalopods: Octopus, Squid, Cuttlefish, and Nautilus · NOAA — Love is in the air, and sea: 5 facts about the affections of marine creatures · Ángel Guerra (2019) — Functional Anatomy: Macroscopic Anatomy and Post-mortem Examination

Where blood gains oxygen, and where it goes

Two branchial hearts push oxygen-poor blood towards the gills. At the gills, the blood takes up oxygen from the water. The hearts move the blood; they do not manufacture its oxygen.

After picking up oxygen at the gills, the blood reaches the systemic heart. This heart sends it throughout the body. Systemic means that it serves the body as a whole.

Three hearts do not divide the body into thirds

Each heart does not serve a separate third of the body. Sending blood to the gills and sending oxygen-rich blood to the body are connected parts of one circulation.

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Sources and scope

Scope of this fact
  • This reading explains the basic structure and function of octopus hearts. Counts do not indicate proportions of blood or body size.
  • The diagram shows relationships in the blood route. It does not depict the position of organs or establish an evolutionary cause for the three-heart arrangement.

Original writing by Rantap