1. Spray a large bowl with nonstick cooking spray. Spray heart shaped pans or 9x13 casserole dish with nonstick cooking spray. Set both aside.
2. Melt butter over medium heat in a large saucepan. Reduce heat to low and stir in marshmallows. Stir until marshmallows melt and mixture is smooth.
3. In bowl sprayed with nonstick cooking spray, combine cereal and marshmallow mixture. Stir until cereal is coated with marshmallow mixture. Press into prepared pans or casserole dish. Let set for 30 minutes.
4. If desired, ice with icing before serving.
If you don't have heart shaped pans, you can use a 9x13 baking dish and then cut into hearts with cookie cutters.
Be sure to coat pans and spoons with nonstick cooking spray before mixing because the mixture is extremely sticky.