Here is a chart that is very helpful to me. If you've never seen it, it may help.
http://shinymetalobjects.net/cake/calculator/cakulator.cgi?option=2&option=Select+Cakulator
Not to freak you out, but I'd be more concerned about the bottom point than the curved top!
Make a template and you should have no trouble carving it perfectly. You may need to take your template to a copy place to enlarge it to the correct size. Be sure to bring an outline of your pans so you can play around with template sizes.
If you're covering in buttercream, I'd suggest freezing the carved cake for at least 40 minutes before icing it. If it doesn't fit in your freezer, then freeze each piece of it separately, then assemble out of the freezer. Don't freeze it solid or it will take forever for the condensation to evaporate.
If you're covering in fondant (or even still if you're covering in buttercream), apply a very thin sheet of fondant to the point of the heart, on the sides (not the top). This will help prevent the cake from tearing while you're icing or crumbcoating it.
Good luck!
For oversize pieces I like to make my template using wrapping paper. It's big, it's white on the back and there's always some around. Then you can skip the copy shop. Make your template the kindergarten old-fashioned way by folding your paper in half first and sketching half a heart and cutting it out. You may find you prefer a more or less rounded shape that way once you see it actual size. And you will definitely see what your shape will look like before you start carving! Good Luck.
Theresa
For oversize pieces I like to make my template using wrapping paper. It's big, it's white on the back and there's always some around. Then you can skip the copy shop. Make your template the kindergarten old-fashioned way by folding your paper in half first and sketching half a heart and cutting it out. You may find you prefer a more or less rounded shape that way once you see it actual size. And you will definitely see what your shape will look like before you start carving! Good Luck.
Theresa
^^agree with everything^^
True, you can skip the copy shop for this project. I guess I got ahead of myself.
freezer paper works well, too, and has the added advantage of being non-stick and a little heavier than gift wrap. I keep freezer paper just for making templates. 
I always fold my templates in half before making any adjustments. That way, no matter what I screw up, at least it's even!
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