Sanders won't get chosen as the candidate for the Democrats. If he does it will be a mistake. They will need to give him a superb running mate if he is picked.
A heart attack will make people really think about choosing him. It should be a disqualifier. Pity people pay doctors to give them the all clear. Or they convince themselves they are fine.
On the right they will be worse with the flak calling him weak and picking at every thing they can like they did with Hillary when she was I'll and looked like she needed a break.