Preheat the oven to 350°F. Grease an 8x8-inch square metal baking pan and an 8-inch round cake pan.
Prepare the cake mix according to package directions. Divide cake mix between prepared baking pans. Bake 25 min., until a toothpick inserted into the center of the cakes come out clean. Cool cakes completely on a wire rack.
Cut the round cake in half. Lay the square cake on a platter with one point facing up to form a diamond. Place semi-circles of cake along top 2 flat sides of square cake to form a heart.
Place strips of parchment or wax paper under edges of the cake. Ice cake with the frosting, covering it completely. Sprinkle candies or sprinkles along the edges of the cake. Remove parchment paper.