It’s fairly straightforward to determine if someone has sustained some sort of heart injury. From Steve Kirsch at stevekirsch.substack.com:
There is a company, HeartCare Corp, that makes a machine that looks like an EKG, but can detect a wide variety of heart damage, including myocarditis. They can assess their team in a day.

Just like Dorothy in the Wizard of Oz could always return to Kansas at any time, the same is true of the Buffalo Bills… if they want to assess whether their players have a heart injury or not, all they have to do is give Heart Care Corp. a call and arrange for a visit to their team.
The HeartCare screening is safe, non-invasive, and takes around 15 minutes.
Then they would know for sure if the COVID vaccine has injured their players. This will save lives.
Sound good?
Does the technology work?
Yes.
They’ve screened vaccinated patients and the rates of clinical and subclinical myocarditis observed is so high you’d never believe I was telling the truth (hint: it’s well over 5% in the general public).