Bake the cake as directed on the box. Cool completely. Once cool, using the straw, put holes all over the entire cake, make sure to go all the way to the bottom of the pan. Pour the can of condensed milk over the cake filling the holes. Repeat with jar of caramel topping. Spread whipped topping over top of cake. Sprinkle Heath Bars on top of whipped topping. Chill in refrigerator.
