Correct, I have a trans male friend who actually had a heart attack and a stroke because of his testosterone therapy and unfortunately for him is now actually not able to take it. I cannot imagine how that would feel, it would really be awful. He wasn't really on it long enough to have irreversible changes either. Like I could stop taking hormones tomorrow (not that I would) and I would still pass as male for the rest of my entire life. My body fat distribution would revert and my face shape would change back and my body composition would be less muscular but I would retain facial and body hair and my voice would stay the same.
Generally, if a trans man has any history of heart conditions they are at risk of being denied treatment until it's managed, if it can be. I got a bit stressed out last year (literally, due to burnout, and for this reason too) when I ended up with mild hypertension due to the prolonged burnout. I was terrified it would impact my HRT and my access to it. My GP kept a really close eye on it and measured my heart stuff every time I saw him though and it's now back to normal, even on the lower side now.
I worry about people who cycle without doing a lot of research into what they're doing. I researched the impact of testosterone on assigned female people for 2 full years before I commenced HRT and read basically every scientific study or article that I could find, reports of bad outcomes, and I got all my checkups done before I started and had my heart checked out by a specialist.
I also know another trans man who literally needs to have blood letting done I think because he produces too many red blood cells. He isn't at a stage where he needs to cease HRT as it's being managed by the blood letting (which is pretty fucking heavy metal I must say) but he knows it's a possibility.