My Dad had a heart attack back in '91. A "moderate" one I guess.
At the time, a year or two into retirement, he had just taken up deer hunting as a sport.
He was pretty down about his heart, of course. We took that interest in deer hunting and used it to get him back on his feet "in time for deer season". He worked hard at rehab, altered his lifestyle. He made the deer season, albeit in limited fashion. It helped him that his docs told him that making the season was an "unrealistic expectation".

He deer hunted a few more years and then moved on to other things.
He's 85 now, still going strong and interested in life.
You just have to "get back up" after you've been knocked down. The deer hunting, in that time and place and
for him was the tool he used to pull himself back up.
Good luck to your F-I-L and the family.