Thanks to Linode Cloud Computing for  supporting this episode of SciShow.

Go to linode.com/scishow to learn  more and get a $100 60-day credit on a new Linode account. [♪ INTRO] Heart attacks are the number 1 cause  of death worldwide in the 21st century. And based on studies of mummies and  written records from various civilizations, this is nothing new: People seem to have been suffering  heart attacks since ancient times.

But for most of human history, heart  attacks were basically a mystery. All anyone knew was that people could  get sudden chest pains and sometimes, but not always, that killed them. Luckily, a lot has changed.

We now have an intimate understanding of  how the heart works, and how it can fail. And how we got here is pretty remarkable.   For most of human history, the  chest was a bit of a black box. It took time for scholars, including  Arab and Renaissance European folks starting around the 1200s, to break down  various cultural and religious taboos around autopsies and make them more of a thing.

By the end of the 18th century, a number  of doctors and scientists had noticed a possible connection between  fatal chest pains and problems in the blood vessels surrounding the heart. For instance, some, like British physician  Edward Jenner, noticed that the arteries that fed the heart could become narrow,  stiff, and full of fatty plaque. This blockage could cut off part or  all of the blood flow to the heart.

And by the late 1800s, this  narrowing of the arteries was recognized as the cause  of fatal heart attacks. This was a huge step forward. But there were still a lot of questions.

Like, doctors kind of assumed this sort  of blockage would always be fatal, so they weren’t sure what was going on in people  who survived this kind of chest pain. Some people had also noticed  the presence of blood clots in these blood vessels during  autopsies, but not always. And it wasn’t clear if clots were a  cause of the heart attack or an effect.

We also didn’t really have a lot of  good ways to investigate these questions in living people, but that changed soon, thanks to both more observation and  a few advances in technology.   One important advance came in the  early 1900s, with the invention and adoption of the electrocardiogram,  known by the initials ECG or EKG. This device records the  heart’s electrical signals. A healthy, working heart would produce  a repeating, predictable pattern on an ECG, but in heart disease  produced different patterns.

This made it possible for doctors to distinguish hearts with heart disease from healthy ones. Another breakthrough came when doctors  discovered they could inject dyes into the arteries around the heart and then  use X-rays to see how blood was flowing. The first time they did this was actually  an accident, and the doctors who did it were afraid that they had killed  their patient, but they did not.

And their discovery would go on to help other  doctors see blockages in living people. Over time, these tools combined  with other lines of evidence proved that people could, in  fact, survive certain blockages. It also gave doctors better ways to  diagnose heart attacks as a specific problem separate from other conditions that can cause  chest pains, like an injured rib or a hernia.

It also helped them identify risk factors  and ways to help people survive attacks.   There was still the question  of those blood clots, though, like the ones Edward Jenner noticed  way back when he was doing autopsies. Like, were they part of the cause? Something that happened later?

What was going on with them? By the 1970s, scientists had started to  believe they might be part of the cause, but a 1980 study really sealed the deal. In it, doctors used X-rays to examine the  hearts of over 300 heart attack survivors, within 24 hours of an attack.

And they almost always found clots  that seemed to clear up over time. That pretty clearly suggested that the  clots were causing the heart attack and not just happening hours  or days after the fact. If they were developing after the attack, the scientists would expect to see  them get worse over time, not better.

So, finally, after centuries of work, scientists  had figured out the cause of heart attacks. It wasn’t always a linear process, but  in the end, we had a clear picture. The heart is fed by blood vessels that  bring oxygen and nutrients to the muscle cells and take away waste, but  these blood vessels can become stiff and narrow over time, often  due to a build-up of plaque.

If this blocks blood flow, or if  a blood clot forms and gets stuck in the narrowed artery, the  muscle cells in the heart can quickly become starved and begin  to die, causing a heart attack. That was over four decades ago, but  even though we can now definitively say what heart attacks are and what causes  them, there’s still a lot of work to be done before they’re no longer topping  those cause of death statistics. Fortunately, what we have learned  makes it possible for doctors to keep an eye out for people  who are developing blockages and offer them ways to protect their  hearts before it is too late.

Which is a good reminder of how  astounding it is to live in a time where we know just so much about the human body. And when there’s so much to know and learn, your time is the most valuable thing you have. And that’s why the sponsor of this  video, Linode Cloud Computing, makes their services as quick  and easy to use as possible.

They have a bunch of one-click apps and services that you can get up and  running in under a minute. But if you want to level up to add  analytics or custom configurations, Linode has tons of guides  and videos to help you out. Their professional services are available  whenever you find yourself running low on time, because they know that you  only have so much of it in a day.

So Linode has professionals  standing by 24/7 ready to help via phone call or support ticket. To get started with Linode and  their professional services, click the link in the description  or head to linode.com/SciShow. That link gives you a $100 60-day  credit on a new Linode account.

Thanks to Linode for supporting this  video, and thank you for watching. [♪ OUTRO]