To prepare, wash and dry the fabric to remove any finishes that might prevent dye absorption and cover up your work surface with plastic.
Note: This technique should work on pretty much any 100% cotton fabric including T-shirt jersey.

Make a pattern for your heart. I traced my 2½" heart onto a plastic sheet, Then I cut it out as a template which can be reused many times.

Cut fabric into 5" squares. Trace the heart shape in the center of fabric using a fabric marking pen.

Using a needle and thread, make a hand running stitch over the traced line, spacing stitches about ¼" apart. Don't knot the tread at the end cause here comes the trick that makes it work.

Pull the end of the thread to gather the fabric on the stitched line, pushing your finger through the center to puff up the fabric. Tie the ends of the thread into a knot and wrap a small rubber band around the thread. Soak in warm water for a few minutes.

Grab some rubber gloves and shake up your dye. Measure and mix ½ tsp Rit Fuchsia dye or Rit Petal Pink dye with 4 cups of hot water in a glass bowl. Stir well. Test your dye color with a scrap of fabric to get your desired shade. You can add more water to lighten the color or more dye to darken the color.

Immerse the wet tie heart in dye bath. Cover with plastic wrap. Line bottom of microwave with paper towels. Place dye in microwave and nuke it on HIGH for 2 minutes.

Carefully remove from the microwave. Rinse the tied fabric in cool water and remove the rubber band and thread. Continue to rinse fabric until water runs clear. Wash in warm water with mild detergent and rinse. Lie flat to dry, iron the fabric and you're ready to adorn away.