The human body can repair skin/organ laceration, fractures, even repair nerves - albeit the duration and rate of recovery differ. For instance:
The burn scar on my arm from the hot soldering iron was smooth earlier, now even the scar has grown hair over it. My rib, having suffered a nasty contusion 7 months ago, still troubles me on occasion almost to the point I must stop aught all. A school-mate who suffered a compound fracture of the tibia is recovered to the point he walks again; albeit with a slight limp.
Why can the heart muscles not repair themselves?