Systemic heartThe main heart, in the middle. It pumps blood that has been through the gills round the rest of the body.
Branchial heartsTwo small hearts, one at the base of each gill. Each pumps blood through its gill.
AtriaTwo thin chambers, one leading from each gill. They bring blood from the gills into the systemic heart.
Vena cavaThe large vein that brings blood back from the body. It forks, and one branch goes to each branchial heart.
AortaThe large artery that leaves the systemic heart. It carries blood out to the body.
Around the hearts 3
GillsTwo feathery organs, one on each side inside the mantle. Blood picks up oxygen from the water here.
MantleThe bag-like body behind the head. The hearts, the gills and most other organs are inside it.
SiphonA tube at the side of the head. The octopus squirts water out through it to swim.
How this list was compiled: Every name checked on 2026-10-01 in two sources. Wikipedia, Octopus (Circulation and respiration) and Branchial heart, https://en.wikipedia.org/wiki/Octopus. Natural History Museum, London, Octopuses keep surprising us, https://www.nhm.ac.uk/discover/octopuses-keep-surprising-us-here-are-eight-examples-how.html. National Wildlife Federation, wildlife guide, Octopuses, https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Octopuses. R. W. Hegner, College Zoology (1912, public domain), the circulation of a squid, https://archive.org/details/collegezoology00hegn. T. J. Parker and W. A. Haswell, A Text-book of Zoology, volume 1 (1910, public domain), the circulation of a cuttlefish, https://archive.org/details/textbookofzoolog00park. Animal Diversity Web, University of Michigan Museum of Zoology, Cephalopoda, https://animaldiversity.org/accounts/Cephalopoda/. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
An octopus hearts diagram, with a window cut in the mantle. An octopus has three hearts: one systemic heart and two branchial hearts, one at the base of each gill. It is a plan, not to scale.
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Follow the blood
Start at the vena cava, which brings blood back from the body. It forks, and each branch leads to a branchial heart. Each branchial heart pumps the blood through a gill, where it picks up oxygen. An atrium carries it from the gill to the systemic heart, and the systemic heart pumps it out through the aorta to the body.
Around the hearts
All three hearts sit inside the mantle, the bag-like body behind the head. The siphon is the tube at the side of the head. The two large vessels are drawn side by side so that both show. Press Quiz me to name each part yourself.
The systemic heart stops beating while an octopus swims, so the animal tires quickly and mostly crawls.
Questions and answers
How many hearts does an octopus have?
Three. One systemic heart pumps blood round the body. Two branchial hearts, one at the base of each gill, pump blood through the gills.
What do the three hearts of an octopus do?
The two branchial hearts pump blood through the two gills, where it picks up oxygen. The systemic heart then pumps that blood round the rest of the body.
Why is octopus blood blue?
It carries oxygen with hemocyanin, a protein that contains copper where our own blood uses iron. The copper makes the blood blue when it is carrying oxygen.
Where are the hearts of an octopus?
Inside the mantle, the bag-like body behind the head. The systemic heart is in the middle, and a branchial heart sits at the base of each gill.