Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch pan.
Mix cake batter according to directions on package. Coat bottom of prepared pan with a layer of marshmallows, then pour batter over marshmallows. Spread cherry pie filling on top of batter layer.
Bake in the preheated oven for 30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool. Serve with whipped topping if desired.
