Bake cake according to directions in a 9x13 pan.
Let cake cool for about 5 minutes.
Poke holes in cake with the handle end of a wooden spoon.
While cake is still warm, slowly pour over sweetened condensed milk over the top making sure some gets in all the holes of the cake.
Next drizzle the caramel topping evenly over the cake slowly, making sure some gets in all the holes as well.
Once cake is completely cooled, Spread cool whip over the top evenly.
Sprinkle with Heath Candy bar pieces.
Store in fridge until ready to eat. Store any leftovers in fridge.