Blockages can be caused in 3 ways:
1. increasing occlusion by plaque formation over time.
2. Sudden occlusion by a clot floating into an arterial lumen of smaller diameter.
3. Plaque rupture and platelet mediated clot formation on site.
Only the first route involves slowly building plaque over time. In the 2nd scenario, you could have no plaque one day, 100% occlussion the next. It isn't plaque causing the clot; the clot migrated to that spot from another sources. (This is why afib pts are on blood thinners - to prevent this very thing.) In the case of #3 above, you could have a 20% blockage one day, and a total occlusion the next.
Platelets tend to be a prime culprit. In a normal system, platelets are heroes to the blood, preserving supply in case of damage to the system and acting as primary spotters for inflammatory situations.
In a diseased system, I've heard platelets referred to as a 'self-perpetuating pathogenic loop'. Platelets form clots by aggregation. The very things that makes them heroes under normal circumstances makes them accomplices under these circumstances. These situations can normally dealt with by thrombolytics: clot busters.
In the 3rd route, above, platelets have inflammatory mediators that can release in and around plaque formations and cause them to become unsteady, or, weak. Once ruptured, platelets attack the ruptured products, creating, in effect, a thrombosed cascade across the lumen of the artery.
This is why primary therapy for AMI is ASA and a platelet aggregate inhibitor, such as plavix or integrillin (rarely, reopro). Both are aimed to reduce platelet clotting by changing the characteristics of the platelet-platelet binding sites.
So, think plavix and asa long term. In addition, B-Blockers and ACE inhibitors are standard post-MI drugs, because they prevent negative cardiac remodeling post MI, and, as a result, reduces the risks of future MIs and decreased Left Ventricular Ejection Fraction over time.
But, there is no reason, assuming a decent EF, that someone can't resume a relatively normal lifestyle after MI. That is patient specific however, and THAT is something your BIL has to get cleared from his doc.