Heat oven to 350°. Grease bottom only of 1 round pan, 8x1 1/2 inches, and 1 square pan, 8x8x2 inches, with shortening. Make cake mix as directed on package, using water, oil and eggs. Pour into pans.
Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes. Run knife around sides of pans to loosen cakes; remove from pans to wire rack. Cool completely, about 1 hour.
Cut round layer in half as shown in diagram. Freeze uncovered about 1 hour for easier frosting if desired. Arrange pieces on serving platter to form heart as shown in diagram. Frost cake with frosting, attaching pieces with small amount of frosting. Store loosely covered at room temperature.