In the real world, one size of heart does not fit all

During rest, the human heart beats between 60 and 80 times per minute, but at the same time, a groundhog's heart beats only 5 times in hibernation, and a hummingbird's heartbeat reaches 1260 beats per minute during flight.

For example, a human heart weighs about 0.3 kilograms, but the weight of a giraffe's heart reaches about 11 kilograms, as the heart must be strong enough to pump blood to the long neck of this animal.

Frogs

Generally, the heart takes deoxygenated blood from the body, sends it to the lungs to get oxygen, and pumps it through the body to supply the organs with oxygen. In humans, the 4-chambered heart keeps oxygenated and deoxygenated blood in separate chambers. But in frogs, grooves called trabeculae (plural trabeculae, meaning "small bundle") keep oxygenated blood separate from deoxygenated blood in a single ventricle.

Mammals and birds have four-chambered hearts, but frogs have three, Daniel Mulcahy, a collaborating vertebrate zoologist with amphibians and reptiles at the Smithsonian Institution, Museum of Natural History in Washington, DC, tells Live Science. Only, with two atria and one ventricle.

"Frogs can get oxygen not only from their lungs, but also from their skin. The frog's heart takes advantage of this evolutionary advantage," Mulcahy added.

According to a study conducted in 1989 and published in the American Journal of Physiology, the strangest heart of frogs that can tolerate freezing is the heart of the forest frog (Rana sylvatica), a type of amphibian whose heart stops completely when the frog freezes during hibernation, then begins to beat again Others within one hour of thawing.

Whales

The heart of the blue whale is the largest of all animals living today. "It's the size of a small car and weighs about 430 kg," says James Mead, curator emeritus of marine mammals in the Department of Vertebrate Zoology at the National Museum of Natural History at the Smithsonian Institution. "Like other mammals, the heart of a whale contains 4 Rooms".

This organ is responsible for supplying an animal as long as two school buses with blood, said Nikki Vollmer, assistant professor at the National Oceanic and Atmospheric Administration's Cooperative Institute. "The walls of the aorta, the main artery, could be as thick as an iPhone 6 Plus, more than 15 centimeters thick. This is a thick-walled blood vessel."

When blue whales dive into the depths of the ocean, their heart rate slows to 4 beats per minute, which helps them extend dive time and may relieve pressure, because a lower heartbeat reduces blood flow to the compressed lungs.

Cephalopods

Cephalopods, including octopus and squid, have 3 hearts each. They are also literally blue-blooded because they contain copper in their blood. “Two humeral hearts on either side of the cephalopods supply the blood with oxygen by pumping it through the blood vessels of the gills, and the systemic heart in the middle of the body pumps the oxygenated blood from the gills through the rest of the organism,” says invertebrate zoologist Michael Fickon at the Smithsonian National Museum of Natural History.

"Just like the color of red rust, the iron in hemoglobin becomes red when it is oxidized," he added. But in cephalopods, oxygenated blood turns blue.

Cockroaches

Like other insects, the cockroach has an open circulatory system that is able to transport blood to a site or sites where it can be oxygenated, and where waste can be disposed of, meaning its blood does not fill the blood vessels.

Instead, blood flows through a single structure with 12 to 13 chambers, says Don Moore, a lead scientist at the Smithsonian National Zoo in Washington, DC. The dorsal sinus, located on top of the cockroach, helps send oxygenated blood to each chamber of the heart.

Cockroaches and other insects breathe through superficial openings in the body rather than the lungs, so "the blood does not need to transport oxygen from one place to another."

Instead, the nutrient-carrying hemolymph is white or yellow, the heart does not beat on its own either, and the lumen muscles expand and contract to help the heart send hemolymph to the rest of the body.

The heart is often smaller in wingless crickets than in flying crickets, Moore says. He added that a cockroach's heart beats at the same rate as a human heart.

Earthworms

Earthworms have 5 pseudopods that wrap around the esophagus. "These false hearts don't pump blood, but rather compress the vessels to help distribute the blood throughout the worm's body," Moore says.

It also does not have lungs, but absorbs oxygen through moist skin. "The air trapped in the soil, or above the ground after rain when the worms stay moist, dissolves into the mucus of the skin, and pulls oxygen into the cells and blood where it is pumped throughout the body," Moore explains. Earthworms have red blood that contains hemoglobin, the protein that carries oxygen, and they have an open circulatory system.

Fish

A study published in the journal Science in 2002 found that zebrafish can fully regenerate heart muscle after only two months of damage to 20% of the heart muscle.

"Humans can regenerate their livers, amphibians and some lizards can regenerate their tails, and frogs given a special mixture of drugs can reconstruct their legs, according to a 2022 study conducted in the journal Science Advances, but the regenerative abilities of zebrafish make them a prime model for studying Heart growth.

However, fish have unique hearts. In addition to one atrium and one ventricle, it also possesses two structures that cannot be seen in humans, namely the "sinus venous", which is a sac located in front of the atrium, and the bulbus arteriosus, which is a tube located directly behind the ventricle.

The bulb arteriosus regulates blood pressure as it flows through the capillaries surrounding the fish's gills. But why does a fish need the bulb arteriosus to regulate blood pressure?

"Because the gills are delicate and thin-walled, any hunter knows, they can be damaged if the blood pressure is too high. The bulb arteriosus itself appears to be a chamber with very flexible components compared to the muscular nature of the ventricle," Moore answers.