There is no single solution for this situation. Fitness and diving issues are difficult for both the diver with a health concern and the resort or dive operator sponsoring the dives. Individuals respond differently to the same disease, and not all divers may have the same physical capabilities after a heart attack (myocardial infarction, or MI).
So, who can dive? Who can't? First, the situation you faced occurs more often than many divers believe. As divers grow older, they may acquire medical conditions or illnesses. Your case involved cardiovascular disease, which is common among older divers. Unless divers are committed to a regular fitness program and periodic medical exams, they may not even be aware that they have a potentially serious cardiovascular problem.
The first sign or symptom of cardiovascular disease can be chest pain - or your first heart attack. DAN diving fatality statistics reveal many cases of sudden death due to cardiovascular disease with no prior history of it. In that regard, a fit diver who has recovered fully after an MI may have less risk while diving than many active older divers.
Usually the diver's personal physician will decide if the diver is capable of full activity without restrictions, including scuba, after a heart attack. A discussion of the issue can be found in Diving Medicine, third edition, edited by Alfred Bove, M.D.
If the diver meets fitness requirements, the physician can recommend diving. However, there is no guarantee that a cardiovascular event will not occur while diving. The resort operator cannot be made responsible for deciding who can and cannot dive when there is a medical issue like cardiovascular disease in question.
Even if DAN is called, our physician would have no knowledge of the health history of the diver. If you know who you are going to dive with on a trip, notify the shop ahead of time to prevent any misunderstanding. If you have health issues, have your physician give you written documentation that you have met appropriate health requirements for diving.