This episode was filmed on October 16th, 2020. You can find our most recent information on the pandemic in the playlist linked in the description.

Although we tend to think of COVID-19 primarily as a lung infection, more and more evidence suggests that we should also be looking out for its toll on the heart. Around the world, doctors have noticed a number of different heart problems in some people with COVID, including muscle damage, inflammation, abnormal heart beats, and blood clots.

In fact, one report from back in May estimated that between 7 and 17% of patients hospitalized for COVID-19 had injury to their hearts. And it may be common in cases outside the hospital, too. Even those we think of as some of the most physically healthy, like professional athletes, may be at risk.

So, scientists are paying attention to this, because the better we can understand how COVID affects the heart, the better we can avoid unexpected consequences down the road. There's one condition in particular that's drawn a fair amount of attention.

It's called myocarditis, and it's a general term for inflammation of the heart muscle. It's often due to viral infection, like an adenovirus or rubella. These viruses can directly infect heart muscle cells, damaging them and using them to create more viruses. This can cause inflammation, and about 1% of the people hospitalized due to acute viral infections have heart injury.

And based on the evidence we have, it looks like SARS-CoV-2, the virus that causes COVID-19, can infect heart tissue as well, though it's not clear if it's the muscle cells themselves, or other nearby parts. Whatever virus causes the infection, the immune system responds, and it can sometimes help prevent the virus from doing damage.

But this can actually also cause myocarditis, because by fighting the virus so hard the immune system itself can end up inflaming the heart. And however it happens, this inflammation can cause trouble. For instance, inflammation can make the heart larger, and being big also makes the heart weaker, so it has to work harder to move blood around a person's body. And it can also cause the heart to build up what's essentially a bunch of scar tissue.

Down the line, these effects can mess up the heart's muscle and electrical systems, and lead to serious life-threatening conditions, like abnormal heartbeats or arrhythmias. They can also cause blood clots if stagnant blood pools in the heart. That raises the risk of strokes and cardiac arrest, and even heart failure, which happens when the heart simple can't pump enough blood.

So scientists and doctors are working really hard to understand how and when all this happens, so they can better look out for it. Unfortunately, though, all of this might be happening without the person realizing it. See, myocarditis itself doesn't necessarily feel like anything. Many people don't feel symptoms at all, and only become aware of it when heart failure occurs.

Even if symptoms do occur, they're generally kind of vague things like fatigue, shortness of breath, chest pain, or heart palpitations, so it's hard to know what they're from. And heart problems don't just happen in severe or even current cases of COVID. A study that did MRIs on the hearts of 26 COVID-positive athletes found evidence of heart inflammation in four who'd either had mild symptoms or no symptoms at all.

Meanwhile, a study from Germany found that of 100 people diagnosed with COVID-19, 60% had heart inflammation, and there didn't seem to be any relationship between that and the severity of a person's illness. Ultimately, the exact numbers on how common this is for COVID patients are still unclear.

But all this seems to suggest that myocarditis may not be related to how sick a person appears, and it may be hard to spot. And one group of people who may be especially at risk are athletes, or anyone who works their heart really hard. And there are a few reasons for that.

For one, there's some evidence that exercise could increase inflammation or increase how quickly the virus replicates. But there's also the fact that the extra strain athletes put on their hearts can increase their risk of triggering an arrhythmia or heart failure well after the infection. Experts have long said that if an athlete gets myocarditis from any virus, they should be pulled from playing for at least three to six months, and pass an exercise test before resuming competitive sports.

And depending on what scientists learn in the coming months, athletes may not be the only ones who should take extra precautions. It may be important to monitor the hearts of everyone who contracts COVID-19, to check for myocarditis. If a person does have it, doctors can try to treat the inflammation with oxygen or medications.They can also warn a person to temporarily avoid activities like sports that might endanger their heart.

That could be a lifesaver for people who might not have even known they were unwell until it was too late. But for now, there's still a lot we don't know, like if there's a pattern to the symptoms, or how long they last. While COVID's toll on the heart isn't the most obvious of its symptoms, it's one we may need to pay a lot more attention to as we learn more about how to cope with this disease.

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