Could easily modify to use anything for the inside shape.
4 FREE Hearts for Coloring by Expressive Monkey. Use the hearts as a way to practice color families, color mixing, or Zentangling just to name a few...Or just have fun making a colorful heart for Valentine's Day.
Preschool Crafts for Kids*: 21 Fun Valentine's Day Animal Crafts for Kids (Can you tell I have a crafty girl looking for "heart projects"?) :o)