Myocarditis has been around year decades if not centuries. It is caused by any viral infection settling into the heart muscle. It can be found and detected with several test by a Cardiologist especially if you advised that you had a viral infection. They know how to treated the infection. Once the infections is gone, the person simply needs to rest and not engage in strenuous exercise or activities for at least six months. The problem is if someone get COVID and they do not see a cardiologist for evaluation. The biggest treat is those that are asymptomatic and never get treated.
It has nothing to do with being "treated". Myocarditis and/or pericarditis can result from a number of viruses, coxsackie being one of the well known culprits. The vast, overwhelming majority of the time, virus-mediated inflammation of the heart muscle or heart lining resolves uneventfully. Very, very rarely a dilated cardiomyopathy may be the sequella which, if severe enough, can result in a sudden cardiac death or congestive heart failure.
Again, this complication can occur as a result of infection with a number of common, well-known viruses; fortunately the odds are extremely low.
Does COVID-19 infection bring a higher risk of long term cardiac complication?
Well, we have accumulated a lot of empirical evidence, given the infection has been spreading around the world since last December (or longer). Millions have been infected (CNN has a running tally on their screen nearly 24/7), including thousands and thousands of younger people, professional and amateur athletes among them.
Has there been a spike in sudden cardiac deaths or congestive heart failure in young persons, including athletes who have continued their sports participation post-infection?
Nope.
If sports participation naysayers were truly concerned about myocarditis, and not simply using this well known complication of viral infections to drive an agends, then they should simply advocate for cardiac evaluation of any athlete who tests positive for COVID-19, symptomatic or not. It would be statistically extraordinarily unlikely to find a single person with a severe dilated cardiomyopathy, but cardiac evaluation would at least be a reassurance to an athlete and his or her family.