They can be as big as a piano or too small to see without a microscope. They may beat as much as 1,000 — or as little as six — times a minute.
They are animal hearts and they’re extraordinary.
Yes, the human heart is pretty astonishing, too. The thing has its electrical impulse, so with enough oxygen it can beat when outside of the body.
But then again, we just have one of them. The octopus has three. And it just gets more amazing from there.
The cheetah is one of the fastest land animals, but its resting heart beat is about 120 beats per minute, similar to a jogging human. Here’s the difference: While it takes some time for a human heart to reach its limit, usually 220 BPM, the cheetah can go up to 250 BPM in just a few seconds.
Really Beat It
The cheetah has a bit of competition, however, with the Etruscan shrew. The smallest known mammal by mass, the Etruscan shrew weighs in at under 2 grams and has a 25 beats per second heart rate. That’s a 1,500 BPM. It’s also kind of cute.
Sizing It Up
The human heart is about the size of a fist — and a cow’s heart is the size of a human head. The largest animal heart is the blue whale’s, which has been weighed at about 400 pounds (and it is not the size of a small car, contrary to popular belief).
But the animal with the largest heart-to-body-mass ratio is somewhat surprising: the dog. Compare a dog’s heart to its body mass and it’s a .8 percent ratio. Almost all other animals — including elephants, mice and humans — have a .6 percent ratio. Another animal with a ratio larger than most mammals is the dog’s ancestor, the wolf.
Sizing it down
The smallest animal hearts belong to the .006-inch long fairyflies. You need a microscope to see its heart, which is a tube running along its back. A new species of fairyfly found in Costa Rica is named Tinkerbella nana.
Room for Growth
The tropical, freshwater zebrafish is a popular aquarium addition, but it’s the animal’s heart that deserves the most attention. It has amazing regenerative properties, quickly closing injuries and mending itself back to almost full function.
That’s why researchers study the zebrafish to uncover possible treatments for heart failure and other cardiac injuries. At the CVM, the zebrafish is helping us unlock some of the mysteries of the human immune system.
Human hearts, like those of all mammals, as well as birds, have four chambers. The heart’s “thump-thump” sound is the four valves opening and closing as they pump blood. But frog hearts have three chambers — two atria and one ventricle (you can actually see how it works in a glass frog).
A Little Help
Actually, all reptiles have three-chambered hearts with one exception. Crocodilian hearts have four chambers, but unlike mammals they have an extra flap that can close to keep blood from going to the lungs. Researchers believe the blood can be sent to the stomach to aid digestion, which is just a smidge helpful when bones are often on the menu.
Dive right in
Many animals decrease their heart rate while diving into water. An emperor penguin’s heart rate dips 15 percent from its resting rate when diving and drops even more during long dives (in between dives it jumps rapidly, likely to replenish tissues with oxygen). A manatee heart rate cuts by half while on a long dive and seals decrease their heart rate from 50 to 80 percent while diving. By the way, seals eat squids, which, like octopuses, have three hearts.
Coming Up Empty
There are also numerous animals with no hearts at all, including starfish, sea cucumbers and coral. Jellyfish can grow quite large, but they also don’t have hearts. Or brains. Or central nervous systems. It’s working for them, though. They’ve been around at least 500 million years.
How … cute?
Pairs of dragonflies and damselflies (damselflies are different than dragonflies and, yes, that’s what they’re called) form heart shapes when mating. The male grabs the female behind its head and the female … uh, how about we just show you a photo?
Sources: The Central Florida Zoo; National Park Service; National Wildlife Federation; Journal of Experimental Biology; National Science Foundation
~Jordan Bartel/NC State Veterinary Medicine