1. Heat oven to 350°F (325°F for dark or nonstick pans). Grease or lightly spray bottoms only of one 8-inch round and one 8-inch square pan.
2. In large bowl, beat cake mix, water, oil and egg whites with electric mixer on low speed 30 seconds; beat on medium speed 2 minutes, scraping bowl occasionally. Batter will be lumpy. Divide batter evenly between pans.
3. Bake 23 to 31 minutes (26 to 34 minutes for dark or nonstick pans) or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans. Cool completely, about 1 hour.
4. Cut round cake in half. Put square cake on tray with one point toward you. Place cut side of each half against one of the top sides of square cake to make a heart as shown in diagram.
5. Tint frosting with a few drops food color. Frost cake with frosting. Store loosely covered.
High Altitude (3500-6500 ft): Follow High Altitude directions on cake mix box for 8-inch pans.