Preheat oven to 350 degrees
Bake cake mix according to package directions - adding in flour, sugar, vanilla and an egg
Spread in a 9 x 13 x 2-inch pan.
Bake as directed until a toothpick inserted in center comes out clean.
While still hot, poke holes in the top of cake with a skewer or large fork.
Pour caramel topping and sweetened condensed milk over hot cake.
Let cake cool completely.
Spread with whipped topping and sprinkle crushed Heath bars over entire cake
Refrigerate until ready to serve.