Cephalopods have three hearts, the heart of a cockroach beats in sync with humans, and the zebrafish can regenerate its heart… and many other fascinating facts you can only discover in the animal kingdom.
Did you know that our hearts typically beat 72 times per minute, while a hibernating animal’s heart only beats 5 times, and a hummingbird’s heart can beat 1,260 times?
The human heart weighs about 0.3 kg, but in a giraffe, it weighs 12 kg—this is necessary for pumping blood through its long neck. However, the animal kingdom has even more incredible secrets.
The hearts of the following animals will surely surprise you:
1. Cephalopods have three hearts
All aquatic species, including octopuses, squids, and starfish, actually have three hearts. Two of these hearts assist in pumping blood, while the central heart regulates blood flow through the arteries to nourish the body.
Imagine if humans had three hearts, how many years would we live?
Interestingly, the blood supplied by these three hearts is not red, as we often think. In fact, the blood of these mollusks is blue due to the presence of copper in their cells. In contrast, human and mammalian blood is red because it contains iron in hemoglobin.
2. Cockroaches: hearts that don’t do the job
Like other insects, cockroaches have a unique circulatory system where blood does not continuously fill all vessels but only circulates through 12 to 13 main channels.
The dorsal sinuses, located at the top of the cockroach’s body, help transport oxygenated blood to the chambers of the heart. However, the heart in this case does not circulate blood throughout the body like the hearts of other animals.
This is because cockroaches and other insects breathe through spiracles on their bodies instead of lungs, so the blood doesn’t need to transport oxygen from one place to another. Additionally, according to expert Don Moore III at the Smithsonian National Zoo, a cockroach’s heart beats in sync with a human heart.
3. Earthworms use “fake” hearts
Earthworms are animals without hearts, but they have five structures called “pseudohearts” surrounding their esophagus. These pseudohearts do not pump blood but merely contract the blood vessels to aid in circulation. Additionally, earthworms do not have lungs; they absorb oxygen through their moist skin.
Earthworms have red blood because they contain hemoglobin, a protein that carries oxygen. However, unlike humans, they have an open circulatory system, so hemoglobin simply drifts among other substances rather than being absorbed or metabolized.
4. Zebrafish can regenerate their hearts
If a zebrafish’s heart is damaged, it can immediately regenerate a new one to replace it. In a study published in a scientific journal in 2002, researchers found that zebrafish could regenerate 20% of their damaged heart tissue within just two months.
Zebrafish hearts regenerate when injured
While the human liver can regenerate and some reptiles or amphibians can regrow their tails, the ability of zebrafish to regenerate their hearts is leading research into cardiovascular development. However, the heart of this fish is quite unique, as it has only one atrium and one ventricle, with two structures entirely different from the human heart.
In other animals, the heart’s role is to transport oxygen throughout the body. However, in fish, the dorsal sinuses transport oxygen back and forth between the ventricle and the atrium. The thinner the ventricle, the thicker the artery wall, and the faster the blood is pumped to the atrium.
5. Whales have gigantic hearts
According to James Mead, honorary president of the Smithsonian Institution, a whale’s heart has four chambers and is known to be the largest in the animal kingdom. It must be an incredibly large and robust heart to pump oxygen throughout such a massive body, comparable to the size of two buses. It is estimated that a blue whale’s heart weighs up to 589 kg, equivalent to the weight of nearly 9 average adult humans (weighing around 70 kg each).
Furthermore, scientists have found that the walls of the major arteries in a whale’s heart are as thick as the length of an iPhone 6 Plus.
6. Frogs have three-chambered hearts
According to researcher Daniel Mulcachy from the Washington Research Institute, most mammals and birds have four-chambered hearts, but frogs only have three chambers, consisting of two atria and one ventricle.
This heart functions to filter the oxygen that the body absorbs, passing it to the lungs for respiration, and then delivering oxygen to all organs.
In humans, the processes of oxygenating blood cells and separating oxygen from these cells are completely distinct, but in frogs, a part called the myocardium keeps these two processes functioning independently within the same ventricle.
According to Mulcachy, frogs not only take in oxygen through their lungs but also through their skin. The frog’s heart operates on its own principles—the oxygenated blood enters the right atrium and exits through the ventricle to the lungs and skin for oxygen. The cells that have absorbed oxygen then return to the left atrium, enter the ventricle, and deliver oxygen to the organs in the body.
