Some claim it causes it, but those are the anti-vaxxers, so who knows.
Could be that it's a reaction to both the vaccine or the virus directly itself, but I haven't heard anything regarding that specifically. Last I heard was in that lingering effect is actually unusual, because with other viruses that have similar reactions, they eventually dissipate after the person gets better.
I never got the vaccine, but apparently I caught covid twice (I wasn't tested), and I've had heart issues since. Has seem to have improved some, but not completely.
Those who are currently experiencing covid shouldn't get the vaccine because of the heart issue, as it may aggravate it.