1Heat oven to 350°F (325°F for dark or nonstick pans). Place paper baking cup in each of 24 regular-size muffin cups. Make and bake cake mix as directed on box for cupcakes, using water, oil and eggs.
2In medium microwavable bowl, microwave white baking chips uncovered on High 45 seconds. Stir; if necessary, microwave in 15-second increments, stirring after each, until chips are melted and smooth. Cool 5 minutes. Stir in frosting until well blended. Immediately frost cupcakes, or pipe frosting on cupcakes.
3Line cookie sheet with waxed paper. In 1-cup microwavable measuring cup, microwave chocolate chips and shortening uncovered on Medium (50%) 30 seconds. Stir; microwave in 10-second increments, stirring after each, until melted and smooth. Place chocolate in small resealable food-storage plastic bag; seal bag. Cut off tiny corner of bag. Squeeze bag to pipe 24 heart shapes on waxed paper. Refrigerate 10 minutes to set chocolate. Garnish each cupcake with a chocolate heart. Store loosely covered.