Octopuses have three hearts

OCTOPUSES

Octopuses have three hearts — and the one that pumps blood through their body stops every time they swim.

Octopuses have three hearts: two branchial (gill) hearts and one systemic heart. Most octopuses crawl rather than swim long distances (consequence of the stopping heart).

where this comes from

ScienceABC, "Why Do Octopuses Have Three Hearts?" (scienceabc.com/nature/animals/why-do-octopuses-have-three-hearts, fetched 2026-07-27): "Why Do Octopuses Have Three Hearts?" OctoNation, "How Many Hearts Does an Octopus Have?" (octonation.com/how-many-hearts-does-an-octopus-have/, fetched 2026-07-27): "How Many Hearts Does an Octopus Have?" Scientific American "Octopus Chronicles," Katherine Harmon, July 13 2013 (scientificamerican.com/blog/octopus-chronicles/octopuses-survive-sub-zero-temps-thanks-to-specialized-blue-blood/, fetched 2026-07-27): "Octopus Chronicles,"

HEARTS

Two hearts push blood through the gills to pick up oxygen

Octopuses have three hearts: two branchial (gill) hearts and one systemic heart. Octopus blood uses hemocyanin (copper-based) instead of hemoglobin (iron-based), turning it blue when oxygenated.

where this comes from

OCTOPUS

But when an octopus fires its jet to escape a predator

The systemic heart stops beating when the octopus uses jet propulsion.

where this comes from

ScienceABC (fetched 2026-07-27): "When an octopus uses jet propulsion to swim — typically to escape a predator — its systemic heart actually stops beating. The muscular contractions required for jet-propelled swimming physically compress the heart, preventing it from pumping." OctoNation (fetched 2026-07-27): "that systemic heart stops beating every time the octopus swims! When the mantle contracts hard to fire that jet, it pinches those drainage channels (called venous sinuses) shut from the outside."

COPPER

it uses copper

Octopus blood uses hemocyanin (copper-based) instead of hemoglobin (iron-based), turning it blue when oxygenated.

where this comes from

Wikipedia, "Hemocyanin" (en.wikipedia.org/wiki/Hemocyanin, fetched 2026-07-27): " (en.wikipedia.org/wiki/Hemocyanin, fetched 2026-07-27) — " PDBe/EMBL-EBI article by Romana Gáborová (ebi.ac.uk/pdbe/articles/what-do-snails-spiders-octopods-and-queen-england-have-common, fetched 2026-07-27): "Octopuses and horseshoe crabs have blue blood because the protein transporting oxygen in their blood, hemocyanin, contains copper, instead of iron" Scientific American (Katherine Harmon, 2013, fetched 2026-07-27): "The copper in hemocyanin makes their blood run blue."

RATHER

So most octopuses crawl along the seafloor rather than swim

Most octopuses crawl rather than swim long distances (consequence of the stopping heart).

where this comes from

spacedaily.com summary (fetched via search 2026-07-27): "many bottom-dwelling octopuses tend to crawl along the seafloor instead of swimming for long stretches" ScienceABC (fetched 2026-07-27): "extremely exhausting"

Go and see

Put your hand on your chest and count your heartbeats. You have one. They have three — and the hardest-working one stops when they run.

What we refused to claim

“"Only 25% as effective as hemoglobin"”

— cited by ScienceABC but not independently corroborated in this fact-check. Exact efficiency ratio not spoken in the script.

“Antarctic hemocyanin cold-adaptation”

— verified (Scientific American 2013), but tangential. Not in scope for these beats.

“"Blue blood even when deoxygenated" nuance”

— technically hemocyanin is colorless/clear when deoxygenated, blue only when oxygenated. The script says "uses copper, which turns it blue" — accurate (standard shorthand used by Smithsonian, Scientific American, NHM) but taken to mean the oxygenated state. Not misleading; no correction needed.

Publishing what we refused to claim is the strongest evidence the rest was checked.