Answer:
A heart attack is caused by a lack of blood flow, due to blockage, in the vessels that surround the heart. Stents are used as a treatment to create a clear path that blood can travel through. However if the heart attack has been left untreated, ie the person did go to the ER for a few days, damage can be done to the heart muscle. If this muscle is deprived of blood for to long the damage can't be reversed. A cure might imply that damage can be undone, and that's not the case.