6 weirdest hearts in the animal kingdom

Hearts have become iconic symbols of Valentine’s Day, but when it comes to hearts in the real world, one size doesn’t fit all, especially in the animal kingdom. At rest, the human heart beats 60-80 times per minute, but at the same time the heart of a hibernating groundhog just beat five times and the heart of a hummingbird reached 1,260 beats per minute during powered flight. The human heart weighs about 0.6 pounds (0.3 kilograms), but a the GIRAFE weighs approximately £25 (11 kg), as the organ must be strong enough to pump blood up the animal’s long neck. Here are some other creatures with strange hearts.

1. Frogs

The organs of the glass frog are visible from the outside. (Image credit: Thorsten Spoerlein via Getty Images)

Mammals and birds have a four-chambered heart, but frogs only have three, with two atria and one ventricle, said Daniel Mulcahy, a vertebrate zoology research associate specializing in amphibians and reptiles at the Smithsonian Institution, Museum of Natural History in Washington, D.C.

In general, the heart takes deoxygenated blood from the body, sends it to the lungs to get oxygen, and pumps it through the body to oxygenate the organs, he said. In humans, the four-chambered heart keeps oxygenated blood and deoxygenated blood in separate chambers. But in frogs, grooves called trabeculae separate oxygenated blood from deoxygenated blood in its single ventricle.

Frogs can get oxygen not only from their lungs, but also from their the skin, said Mulcahy. The heart of the frog takes advantage evolutionary oddity. When deoxygenated blood enters the right atrium, it enters the ventricle and exits to the lungs and skin to get oxygen.

Oxygenated blood returns to the heart through the left atrium, then through the ventricle and to major organs, Mulcahy said.

Even weirder are the hearts of frost-tolerant frogs, including the wood frog (Lithobates/Rana sylvaticus), whose heart stops completely when the frog freezes during winter hibernation, then starts beating again within an hour of thawing, according to a 1989 study in the American Journal of Physiology.

2. Whales

This life-size model shows the enormity of a blue whale’s heart. (Image credit: © AMNH/D. Finnin)

the blue whale heart is the largest of all living animals today. “He’s the size of a small car and weighed in at around 950 pounds. [430 kg]said James Mead, curator emeritus of marine mammals in the Department of Vertebrate Zoology at the Smithsonian Institution’s National Museum of Natural History. Like other mammals, the whale’s heart has four chambers.

The organ is responsible for supplying blood to an animal the length of two school buses, said Nikki Vollmer, an assistant scientist at the Cooperative Institute for Marine and Atmospheric Studies working with NOAA Fisheries Southeast. “The walls of the aorta, the main artery, can be as thick as an iPhone 6 Plus is long,” more than 6 inches (15 centimeters), Vollmer told Live Science. “It’s a thick-walled blood vessel!”

When blue whales dive deep into the ocean, their heart rate slows to four beats per minute, which helps them extend their dive time and can even alleviate decompression sickness, known as bends. This is because this lower heart rate reduces the passage of blood to the lungs under pressure and the reduction in the hand of nitrogen absorption can smooth out bends, a 2021 study in the journal Comparative biochemistry and physiology Part A: Molecular and integrative physiology reported.

3. Cephalopods

Applaud warmly the Boreal Aonius the three hearts of the squid. (Image credit: Michael Vecchione)

There is nothing mixed about cephalopods. Those sprawling and cocked sea ​​creatures, including octopussquid and cuttlefish, have three hearts each.

Two brachial hearts on either side of the cephalopod’s body oxygenate blood by pumping it through blood vessels in the gills, and the systemic heart in the center of the body pumps oxygenated blood from the gills through the rest of the body, Michael said. Vecchione, an invertebrate zoologist at the Smithsonian’s National Museum of Natural History.

Cephalopods also literally have blue blood because they have the copper in their blood. Human blood is red because of the the iron in hemoglobin. “Just like rust is red, the iron in our hemoglobin is red when oxygenated,” Vecchione said. But in cephalopods, oxygenated blood turns blue.

4. Cockroaches

The cockroach’s heart beats at about the same rate as a human heart. (Image credit: Paul Starosta via Getty Images)

Like other insects, the cockroach has an open circulatory system, which means that its blood does not fill the blood vessels. Instead, blood flows through a single structure with 12 to 13 chambers, said Don Moore III, senior scientist at the Smithsonian’s National Zoo in Washington, DC.

The dorsal sinus, located at the top of the cockroach, helps send oxygenated blood to each chamber of the heart. But the heart isn’t there to move around in oxygenated blood, Moore said.

“Cockroaches and other insects breathe through spiracles [surface openings] in the body instead of the lungs, so the blood doesn’t have to carry oxygen from one place to another,” Moore said.

Instead, the blood, called hemolymph, carries nutrients and is white or yellow, he said. The heart does not beat on its own either. The muscles in the cavity expand and contract to help the heart send hemolymph to the rest of the body.

The heart is often smaller in wingless cockroaches than in flying ones, Moore said. The cockroach’s heart beats at about the same rate as a human heart, he added.

5. Earthworms

Earthworms have five pseudo-hearts. (Image credit: Gail Shotlander via Getty Images)

The earthworm cannot take courage, because it has none. Instead, the worm has five pseudo-hearts that wrap around its esophagus. These pseudo-hearts don’t pump blood, but rather they squeeze vessels to help circulate blood throughout the worm’s body, Moore said.

It also has no lungs, but absorbs oxygen through its moist skin. “Air trapped in the ground, or above ground after a rain when the worms can stay moist, dissolves into the mucus in the skin and oxygen is sucked into the cells and blood system where it is pumped around the body,” Moore said.

Earthworms have red blood that contains hemoglobin, the protein that carries oxygen, but unlike humans, worms have an open circulatory system. “So the hemoglobin kind of floats among the rest of the fluids,” Moore said.

6. Fish

A zebrafish can regenerate its heart. (Image credit: Mirko_Rosenau via Getty Images)

If a zebrafish is heartbroken, it can just push one away. A study published in 2002 in the journal Science discovered that zebrafish can completely regenerate the heart muscular only two months after 20% of their heart muscle was damaged.

Humans can regenerate their liveramphibians and some lizards can regenerate their tails, and frogs given a special drug cocktail even regrow their legs in a 2022 study in the journal Scientists progressbut zebrafish’s regenerative abilities make it a prime model for studying cardiac growth, Moore said.

However, fish have a single heart. In addition to an atrium and a ventricle, fish also have two structures that are not seen in humans. The “sinus venous” is a sac that sits in front of the atrium and the “bulbus arteriosus” is a tube just behind the ventricle.

As in other animals, the heart circulates blood throughout the body. Deoxygenated blood enters the sinus venous and flows into the atrium, Moore said. The atrium then pumps blood into the ventricle.

The ventricle has thicker and more muscular walls and pumps blood into the bulbus arteriosus. The bulbus arteriosus regulates the pressure of blood as it flows through the capillaries surrounding the gills of the fish. It’s in the gills that oxygen exchange takes place across cell membranes and into the blood, Moore said.

But why does the fish need the arterial bulb to regulate arterial pressure?

“Because gills are delicate and thin-walled – any angler knows that – and can be damaged if blood pressure is too high,” Moore said. “The bulbus itself is apparently a chamber with very elastic components compared to the muscular nature of the ventricle.”

Editor’s Note: Originally published February 13, 2015 and updated February 14, 2022.

Originally posted on Live Science.

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