Secret to flat cakes: wet cake strips (i., Bake Even Strips) and wrap around the cake pans. They act as an insulator to help the cake bake evenly (flat). You can also use strips of towel: drench, wrap around the pans, and bake.
If you like the idea of the heart cake, but want something a little less formal, a poundcake is just as impressive! The technique behind it is completely different, using a heart shaped cookie cutter to get your surprise heart design.