We wen
You've said this many time and that's the way it was in the sixties and 70s before scanners.
However, now, with multiple scanners in big hospitals and different types, and pushing camera's up from the wrist area into the heart, they can see what % Plaque, and stent an artery, they can see the valves and replace them, etc so there are less surprises.
What they do after surgery now is send the patient to regular clinics where they do quite heavy work outs; from what I saw heaveier than Stress ECG, so if you are interested in heart it would bve well worth a look at what happens today. For a start not too many die in their 50s and 60s like they used to.