Step 1: Supplies
Puff paint optional
Sewing machine or could easily be stitched by hand
Step 2: Marking The T-shirt Lines
Cut the lines.
Go back and cut uneven cuts along the trimmed edges as shown.
Step 3: Cut Square From Contrasting t-shirt
Please note: The paper heart is shown just for illustration purposes only.
Step 4: Pinning
Smooth out the red fabric and pin it to the t-shirt through all layers.
Step 5: Sewing Heart Outline
Step 6: Trimming The Insert
Very carefully trim the heart shape (using the stitching lines of the heart shape; as a guide) to remove excess fabric.
Please note: I forgot to take a picture before the lines were sewn.