Some time in 2021 there was a story about COVID vaccines and heart issues here on HN. The comments filled up with people saying that ever since they'd got their shots they were experiencing new heart-related symptoms they'd never had previously like permanently racing heartbeats, palpitations/fluttering, inability to do exercise and more. Unfortunately I'm not sure how to re-find that discussion. I also have a good friend who works in IT who had a heart attack in the weeks after his shots, but he refused to believe that's what happened and never went in to get diagnosed (the symptoms were an exact match however).
Some rough calculations indicate the numbers affected by this kind of (hopefully) low level heart damage seem much higher than claimed. They say of the "hundreds of millions" of shots there are only 1000 cases of diagnosed heart damage from the vaccines. Call it 1000/100,000,000 or one in a million. There are approx 5M readers of Hacker News per month, so far less per day. Of those only a tiny handful have accounts and post comments. If their numbers are right then there should be ~no HN commenters with post-vaccine heart problems but this thread filled up with people posting their own experiences of such a thing.
Then there's also the other health problems. My gfs friends who took it have been complaining that they seem to get sick with colds/fluey things way more frequently since the shots, I heard similar complaints from a couple of old coworkers. One of those girls complaining of frequent sickness also reported disrupted menstruation but the doctors have ignored it all because as far as they are concerned, the vaccines are 'perfectly safe'.