I'd like to take credit for thinking of this but I can't. I do however think it's very clever and would like to pass the tip onto you.
If you'd like to make a heart shaped cake for your Valentine, all you have to do is to make one square and one in a round pan. When the cakes are baked and cooled, cut the round cake in half and place those halves on the right angle of the square, one on each side, frost and there's your single layer heart cake. ( and you thought algebra and math weren't ever going to come in handy, it's a good thing someone was paying attention! )