What Happens To Your Heart When You Get Scared

You've felt that thump-thump-thump of your beating heart when frightened. Most times, it's just a small shock when someone sneaks up behind you. But other times, it's a feeling of intense fear, when you think your heart is going to leap out of your mouth, and you hear your pulse drumming in your ears. That's a lot of stress to place on your heart. Did you ever wonder what happens to your heart when you're frightened? And did you ever wonder if the fear becomes so overwhelming that it could literally scare you to death?

If you haven't before, maybe you're wondering about it now.

Fear is a natural emotion that arises from the nervous system and gives us the survival instincts to keep ourselves safe from danger. A frightening stimulus triggers the brain to produce a rush of adrenaline — part of the protective mechanism called the fight-or-flight response (which can include freeze as well), according to Scientific American. In this state, the autonomic (involuntary) nervous system responds and the whole body is put on alert. 

Heart rate and blood glucose levels increase, blood flow is directed toward to the major muscle groups, lungs and pupils dilate, digestion slows, perspiration is triggered, and even the liver and pancreas are affected (per the American Heart Association). Meanwhile, the brain assesses the threat and decides on a course of action (per Medical News Today). These physical changes improve a person's chances of surviving in a life-threatening situation, whether they fight, flee, or freeze.

Although fear causes an all-hands-on-deck response in many systems and organs, the body has a way to calm things down if the threat is found to be innocuous. The parasympathetic nervous system (PSNS) takes over by lowering the heart rate as well as stemming the flow of adrenaline (per Business Insider). So if the perceived threat turns out to be a friend in a costume, not an intruder, the body relaxes. Without the PSNS, the rush of adrenaline would continue and, in large amounts, adrenaline is toxic — particularly to the heart.

Whenever you're scared by a particularly wild amusement park ride or a thriller at the movies, the PSNS will easily talk your body down. Not only are you expecting to be scared, but the adrenaline surge is stopped, so all systems quickly return to normal.

"Swings of emotion and roller coasters are OK for people who are young, who have a healthy heart," Dr. Mark Estes, a cardiologist and professor of medicine at the University of Pittsburgh Medical Center told the American Heart Association. In fact, it's believed that occasional adrenaline rushes may lead to increased cognitive function. Here, we come, Halloween 35!

More dangerous adrenaline surges occur in life-threatening moments, such as suddenly being cornered by an assailant on a dark street — particularly when a person is not entirely heart-healthy. "It's the sudden, unexpected things which tend to cause a dramatic increase in heart rate and blood pressure and put people with pre-existing cardiovascular disease at risk," Dr. Estes said.

Experts agree that it is possible for someone with pre-existing conditions to be scared to death. In genuinely perilous situations, when a flood of adrenaline overwhelms heart-muscle cells, the muscle stiffens and can't relax. Furthermore, a specific system of muscle and nerve tissues, which sets the heart's rhythm, can go into an abnormal beat that can't sustain life. One arrhythmia, ventricular fibrillation, which causes the lower chambers of the heart to vibrate in a way that interferes with their ability to pump blood, is likely the cause of sudden deaths from fear.

Extreme fear can also lead to takotsubo cardiomyopathy, a condition generally known as broken-heart syndrome. In this condition, the left ventricle, the heart's main pumping chamber, is stunned by a surge of hormones (such as adrenaline) that triggers changes in muscle cells or coronary blood vessels, preventing the left ventricle from pumping effectively, according to Harvard Women's Health Watch. Its symptoms resemble those of a heart attack, but tests have shown that in this condition, there's no evidence of coronary artery blockages.

Broken-heart syndrome occurs mostly in women between the ages of 58 to 75. Almost all recover fully within 2 months.

There's no way to avoid fear in life, since there's no way to entirely avoid scary things. What's more, there's no foolproof way to prevent dying from fright — but being in good shape might help. Those who exercise regularly may be better able to handle adrenaline rushes due to their cardiovascular fitness. It's believed that exercise helps temper the body's response to adrenaline.

If you have a pre-existing cardiovascular disease, though, it may be better to avoid environments where you might be "suddenly stressed," suggested Dr. Estes. That might mean saying goodbye to roller coasters, slasher movies, and friends who play practical jokes.

In all honesty, however, experts say sudden death due to fright can happen at any age and to otherwise healthy people. But it is rare, so it's best not to fear fear itself.

Finally, even if you managed to avoid everything scary, you should know that any extreme emotion — be it happiness, sadness, religious (or sexual) passion — can lead to fatal heart rhythms. And avoiding all those emotions would do more harm than good.