Preheat the oven to 350 F. In a large bowl, mix cake mix with oats, peanut butter, eggs, and vegetable oil until smooth. Fold in the Reese's pieces.
Use a cookie scoop to place the cookies onto a large ungreased baking sheet at least 2-inches apart. Bake for 10-12 minutes. Remove from the oven and place one heart on each cookie.