3 Creatures with More than One Heart

The presence of one heart is ingrained into our idea of biology. Our own bodies as well as those of many organisms we see around us have a single cardiac organ. But some buck the trend. Here are a handful of animals with multiple hearts.

1. Octopus and Squid

These similar creatures are both cephalopods and have three hearts in total; one systematic organ to go along with two “gill hearts” that force blood to the gills.

2. Earthworms

While it is not technically a heart, the aortic arch of the earthworm performs a similar function and is commonly referred to as one for the sake of simplicity. An earthworm has five arches/hearts that are segmented and pump blood throughout its body.

3. Hagfish

Who knew such a nasty creature could have so many hearts? The hagfish has four of them: one main three-chambered systematic heart and three accessory pumps.

Bonus: Humans

Yes, there are humans with more than one heart: those who have undergone a “piggyback” heart transplant operation that adds an extra heart as opposed to replacing the original. The latter continues to function, but at a much lower level, while the transplant heart takes over most of the heavy lifting. One person who had the procedure as a baby later had it reversed, and when the second heart was removed, her own was able to take back the reins.

A version of this story ran in 2013; it has been updated for 2022.