Mix pancake mix, cocoa powder and sugar in large bowl until well blended. Stir in buttermilk, eggs and vanilla just until blended. Divide batter equally among 2 bowls. Stir food color into 1 of the bowls.
Pour 1/4 cup of batter per pancake onto preheated ungreased griddle or skillet. Cook 2 to 3 minutes per side, turning when pancakes begin to bubble.
Using a 2 1/2-inch wide heart-shaped cookie cutter, cut out hearts from each pancake. Place a contrasting color heart cut-out into each pancake.