Draw your heart design on cardboard with glue. Draw at least 4-6 lines inside the heart and 8-10 lines outside the heart in the negative space to create shapes.
Let the glue fully dry.
Cover the raised and dry glue with tin foil.
Press the raised design carefully.
Fold the edges around the back.
Use colored permanent markers to design your tin foil art.
Notes
Be careful not to push too hard with the markers or your fingers. You do not want the tin foil to rip.
You can experiment with rubbing alcohol on your permanent markers for an excellent blending effect.
Using a contrasting color scheme will make your heart stand out.