10 Amazing Facts about Heartbeats That You Will Hardly Believe

Two sounds that can be heard in many TV shows and movies are the bleep of a hospital heart rate monitor and the quick, damp thud of a heart beating fast with fear. People can understand what these sounds mean even if they are not watching what is going on. That is because heartbeats are a signal, and despite their simplicity, they actually provide the world with a wealth of information.

Distinguishing life from death and fear from calm is only the tip of the iceberg when it comes to interpreting pulse, and scientists have recently started to scratch beneath the surface. They have discovered that there is much to be learned and even predicted by cracking this simple code. From how they set a limit on human longevity to how they are different in criminals and special forces soldiers, here are ten hard-to-believe facts about heartbeats.

Related: 10 Alternate Medicines That People Swear By

10 Most Mammals Only Get One Billion Heartbeats

Not all animals have hearts. Among those that do not are the immortal jellyfish and the sea anemone. The former can age in reverse and possibly live forever, while the latter can regenerate. Such abilities seem to be off-limits to creatures with a pulse; if something has a heartbeat, it will naturally die at some point. Science might even be able to predict when.

Research has shown that most mammals get about one billion heartbeats. The reason that large mammals like elephants can live into their eighties while small ones, such as rabbits, only live about three years seems to be related to the fact that rabbits’ hearts beat a lot faster. Despite the huge difference in how many years they live, both average out at around a billion heartbeats.

This likely used to be the case for humans, too, but advances in medicine and hygiene have meant that most people today get over two billion heartbeats. This does not mean people should stop exercising, though. The short increase in heart rate will be countered by the lower resting heart rate a healthy lifestyle leads to.^[1]

9 Feeling Scared Does Not Cause Hearts to Race

Surprisingly, it is more likely to be the other way around. A heart rate quickens not because somebody feels scared; instead, it causes them to feel scared. Seeing a possible threat creates a rush of adrenaline in the body, which can even happen before a person is conscious of what they are looking at. The brain receives the information that the heart has quickened and interprets it as feeling scared. But it could also be interpreted as excited or nervous, depending on what is happening outside. It puts all the pieces together like a puzzle to produce an emotion.

The process of receiving inputs from inside the body, like a quickened heart rate, is called “interoception.” It is difficult to study, but it has been demonstrated in mice that a fast heart rate can cause anxiety. A 2023 study out of Stanford University used a special pacemaker to control the heart rate of mice. Those with higher heart rates were less likely to explore a maze to find water, but only when there was also a threat, like the possibility of a small shock.^[2]

8 Music’s Effect on Heart Rate Depends More on Preference Than Genre

“Exteroception” is the scientific term for sensations that are caused by something outside of the body. It is caused by the things that people see, smell, touch, taste, and hear, like music. The effect of listening to music is actually a nice demonstration of how complex the human body and heart rate is. Music is heard and processed by the brain, which can cause people’s heart rate to slow.

Sound processing actually starts in the same area of the brain that controls heartbeats and breathing, called the brainstem. But remember that the brain also receives and interprets heartbeat data through interoception. Perhaps those slower heartbeats help make people feel relaxed when listening to their favorite music, and for the best effect, it does have to be music they like.

Rock music does not necessarily get people amped up, and classical is not necessarily calming. Research suggests that music therapy patients benefit more when they pick the music, and a study that used music to relax arteries found that results were better when rock music fans listened to rock. Likewise, for classical fans.^[3]

7 The Apollo 11 Crew’s Heartbeats Were Tracked

Directors might add a heartbeat sound to help set pulses racing in a movie scene, and those in the NASA control room on July 20, 1969, probably experienced a similar effect. The Apollo 11 crew had their heart rates tracked all the way through their trip to the Moon and back, revealing much about how they felt at each point in the journey.

As might be expected, pulses were heightened during the launch, with Neil Armstrong’s reaching about 110 beats per minute, but it would later soar much higher. The landing on the Moon’s surface was supposed to be automated, but an error forced Armstrong to bring it down manually. His heart rate as he did so shot up as high as 150 bpm. That is about 80% of the maximum for his age and similar to a period of intense exercise. He would hit these heights again later, partly as a result of actual exercise as he speedily collected samples and took photos during a 10-minute excursion on the Moon’s surface.^[4]

6 A Baby’s Heartbeat Does Not Indicate Its Sex

While there is a lot to learn from heartbeats about the stress of space exploration, something they cannot teach anyone is the sex of a fetus. There has been a persistent myth among some people that the heart rate of a fetus reveals whether it will be a boy or a girl; a heartbeat under 140 bpm predicts that the baby will be a boy. The reason people find this idea exciting is that fetal heartbeats can be detected long before an ultrasound can be carried out to determine a baby’s sex.

But sadly for those pinning their hopes on the speed of a pulse, no studies have shown a significant difference in heart rate between male and female fetuses. It is one of many methods which are purported to predict a baby’s sex early on. Others include the shape of the pregnancy bump, cravings for particular foods, and whether the mother experiences morning sickness. None are reliable, and those expecting will just have to wait patiently for the 18th week or later when experts can actually make an informed and accurate guess.^[5]

5 An Expecting Mother’s Heartbeats Could Reveal Delivery Date

While a baby’s tiny ticking heart does not reveal whether it will be a boy or a girl, heartbeats might help predict whether it will be born early. Preterm births are when babies are born before 37 weeks, and they can lead to complications in their health and development. As with many problems, spotting and treating them earlier is better than dealing with a nasty surprise later, and some scientists think that the mother’s pulse could help spot possible preterm births several weeks before they happen.

When expecting mothers wore a device on their wrist to continuously monitor their heartbeats, studies showed that their heart rate variability—tiny changes in the amount of time between their heartbeats—decreased during pregnancy until around seven weeks before they gave birth. It would then start to increase again until their child was born.

This reversal was found in both term and preterm pregnancies, and it correlated with weeks until birth. That means that the more heart rate variability increases, the closer the baby is to being born. It is possible that by looking out for this reversal, the outcomes of premature births can be improved by helping doctors to act sooner.^[6]

4 Elite Olympic Shooters Pull Trigger Between Heartbeats

All competitive sports have an element of psychology to them, and shooting is no different. In fact, that is what it comes down to at its highest level, possibly more than in any other sport. Elite shooters obviously all have the ability to aim and pull the trigger; that is the technical side taken care of. They cannot interfere with each other while shooting, so their biggest enemy as they take aim is themselves. And their heart.

When trying to hit a 0.5mm ring from 10m away, the tiniest disturbance, like a barely perceptible heartbeat, could make all the difference. Being just a fraction of a millimeter off could cost an elite shooter a medal. To avoid such mishaps, they pull the trigger between heartbeats. This is no mean feat when their pulse is racing at up to 160 beats per minute—almost three times per second—because of the pressure.

To do it requires a level of concentration possessed by few people, and even those who can do it cannot sustain such concentration for long. Shooters learn to instantly switch their focus when taking a shot and turn it off in between shots.^[7]

3 Bomb Disposal Experts Have Slower Heartbeats When Working

If the intensity of shooting in a silent room can send heart rates soaring without any real danger, then imagine what must happen inside bomb-disposal experts on the job when a single tiny slip-up could cost them their lives, their limbs, and probably both. Surprisingly, it is not what most people would expect to happen.

A Harvard researcher who studied bomb disposal operatives with more than 10 years of experience found that when they had to concentrate hard on the job, their heart rates remained stable. In other words, the pressure did not get to them. This was likely a result of their years of experience and their meticulous training and preparation. However, this was only half of the story.

The researcher also divided the operatives into two groups: decorated and undecorated. He then discovered that the heart rates of the soldiers with medals, the best of the best, actually dropped when they got down to business. They entered a sort of meditative state. What caused this was, apparently, confidence. Self-belief was the significant factor that separated the best from the rest.^[8]

2 A Low Heart Rate Might Cause Criminal Behavior

Bomb disposal experts put theirs to good use, but low heart rates are also a characteristic of criminals, according to several studies. One looked at the heart rates of more than 700,000 18-year-old Swedish men and their subsequent criminal records. The men with the slowest resting heart rates were 49% more likely to become violent criminals than those with the fastest, and they were 33% more likely to commit a nonviolent offense.

The researchers controlled for many other factors, which means that heart rate was likely the direct cause of this effect. Exactly why this happens is unclear, but it has been suggested that men with lower heart rates do not feel physiological arousal as strongly. They might try to find excitement by doing something illegal, or they may not feel as scared or anxious as others.

So, should those with low resting heart rates be worried? The answer is no. Like how all thumbs are fingers but not all fingers are thumbs, criminals with low heart rates do not mean people with low heart rates are criminals. Over 94% of the men in the study were never convicted of violent crimes.^[9]

1 The Song “Another One Bites the Dust” Gets Hearts Beating Again

Precise, numerical heart rates are necessary for scientific research, but they are not so useful when making recommendations for the man or woman on the street. This is starting to change; smart watches now let people monitor their own heart rates, and people are becoming familiar with the heart rate “zones” used to describe the intensity of exercise. But it would not be helpful to tell somebody about to perform chest compressions, in a literal life or death situation, that they need to go at 100-120 beats per minute.

Luckily, as many folks who have taken a CPR course will know, the Bee Gees have the answer. Their 1970s hit “Stayin’ Alive” is just the right tempo for chest compressions, not to mention lyrically appropriate and catchy. However, there are plenty of other famous songs that fall within the 100-120 bpm range. Other appropriately-named choices include Michael Jackson’s “Beat It” and Fleetwood Mac’s “Don’t Stop.” Or, for those who enjoy a little irony, “Achy Breaky Heart” and “Another One Bites the Dust” also work. ^[10]