Mix the red jello and 1 cup of boiling water in a large measuring cup or small bowl until completely dissolved. Stir in ¼ cup of cold water and ¼ cup of chilled vodka.

Spray a 5x5 inch or similar size container with cooking spray and pour in the prepared jello. The jello should be about 1 inch in depth. 

Place the jello in the refrigerator for 2 hours or until completely set. 

Once the red jello has set, mix the green apple jello and 1 ½ cups of boiling water in a large measuring cup or small bowl until completely dissolved. Stir in ¾ cup of cold water and ¾  cup of chilled vodka.

Set the jello aside to cool completely to room temperature.

While the green jello is cooling, arrange 20 (2-ounce) shot glasses on a rimmed tray or baking sheet.

Remove the red jello from the fridge, run a butter knife around the container's edge to loosen it, and turn it onto a cutting board.

Use a 1 or 1 ½ inch heart-shaped cookie cutter to cut 20 hearts from the slab of jello. You want to use a small enough cutter to ensure the jello hearts fit in the shot glasses.

Place one jello heart in the center of each shot glass. If the green jello is still cooling, place the tray with the shot glasses back in the refrigerator until the green jello has cooled.

Carefully pour the green jello into the side of the shot glasses, filling to be level with the heart.

Place the tray back in the refrigerator for at least 2 hours or until the jello has set. 

Serve chilled.