Create a Template

Fold a small piece of scrap paper (I used a paper bag) in half and draw half a heart on the fold. The heart should be about 2-inches tall.

Cut out your template.

Prepare The Card

Fold one of the cards in half width wise and place your template at the top of the fold. Make sure that the template actually goes a little beyond the fold, so you can keep both sides of the card together.

Trace around the template.

Cut out the heart shape.

Using your 1/8th-inch hole punch, punch holes all the way around the front of the heart card. Try to get the holes fairly close to the edge and fairly close together. 

Crochet the Edge

Working on the outside of the card, pull a loop through a hole with the crochet hook.

Crochet with a slip stitch through the holes as shown below. 

Stick your hook through the next hole,

 and hook your working yarn (not your yarn tail!), 

pull this yarn loop through the hole, 

and then pull it through your first loop.

Do this all the way around the front of the card.

When you get back to where you started pull the live loop to the wrong side of the card. Cut your yarn and pull it through the loop. Tape the ends down and you're done!