Sorry, mine came as a set of two. A 12' and a 8' heart pan. I am not sure what you mean by heating core? Mine are baking pans and go in the oven...
Anyway any recipe I have is for the two of them so you can stack one on top of the other, makes a cool looking cake. Maybe you can do something like that with the leftover batter? Maybe bake it in whatever small pan you have that will fit it, then cut it up after cooking into other shapes, like an arrow to go thru your heart cake.
Think Ace of Cakes style, outside of the box ;)