Cut a heart out of the front of the sweatshirt.
I used a door sign as a model to make a heart large enough.
Cut a heart out of some contrasting material. The heart needs to be 1/2 an inch bigger than the heart you cut from the front of the sweatshirt. Cut 3/4 inch strips from felt.I ran a stitch down the center and them pulled the string to make the ruffles. You can also set your sewing machine to the longest stitch length and the highest tension. When you sew the strips, holding your hand behind the preset foot, they will automatically ruffle.
Place the ruffled heart under the cutout on the front of the sweatshirt and pin in place. Sew in place, moving your machine slowly and lifting up on the presser foot frequently so the sweatshirt will not stretch out of shape. Make sure you are catching the ruffled heart under the stitching.