I'm sure you know the rule-of-thumb based that 220 - age is the maximum. This is not an absolute number, just a ball park number. That said, anyone who has heart disease should check out aerobic activity with their heart doctor.
I have in past years exercised at near my maximum HR, around 90%, but as I now have AFib that isn't something I do any longer, not with my knowledge anyway. When I exercise, or even engage in a physical activity like mowing the lawn, I wear an exercise pulse rate monitor. When I get near 150 bpm, I slow down.
Sorry, these questions are not orthopedic sports medicine questions.