Step 1: Trace and cut out the heart
Trace out a heart with a pen or pencil on your felt on only one side. The outside edges of this heart should reach slightly less than halfway into your palm (see next step for how it looks).
Cut the heart directly down the middle.
Step 2: Pin heart onto gloves
Turn over the heart pieces so that the line you traced in the last step doesn't show.
Position the gloves in your work area so that the thumbs are facing outward.
Position and pin down the heart pieces on the gloves furthest away from the thumbs. The edges where you cut the heart should be facing each other. Don't pin them directly on the edge of the gloves because when you put your hands in the gloves will expand and half of your hearts will disappear.
Try on the gloves to see how they look on your hands when you bring them together to form the heart. You may have to adjust them up/down or left/right. If this is needed, don't move the felt around while the gloves are on. I found this to be too difficult and the felt kept falling down. Instead, take note of approximately how much you need to move each heart piece around, take the gloves off, and reposition them.
Step 4: Stitch heart pieces onto gloves
Thread your needle.
Start stitching from the inside of the glove on the bottom of the felt. Make these stitches about 3/4cm long. For every stitch you make, stitch over it once again to get a bolder, white look. I really like this bold look. If you're using embroidery thread, you only need to stitch once for this thickness. But, for normal thread, we'll need to stitch twice.
Stitch all the way around until your finished with the heart piece.
Step 5: Sew "wiring" into place
While wearing the gloves, touch your hands together to form the heart. Try your best to find our where the best point of contact is between your hands. Mark this area with a pin.
Flip the glove for the right hand inside out and sew down the battery holder. Be sure the positive and negative side corresponds with the schematic.
Now, begin to sew the circuit down starting with the positive line coming from the battery. You don't need to start here, but it's the easiest to do, so we'll practice with it.
I found it easier to sew with the glove inside out. So I also included a schematic of how the circuit should be sewn in from the inside. The gloves I used had enough stitches for me to be able to sew in the thread and not have it show up on the opposite side. If you can do this, it will make for a nice, clean look on your gloves. The trick is not to poke the needle in too far.
Once you get to the edge, you should be able to see the pin you placed to signify the point of contact with your hands. This part can get tricky. Sew the thread in 1cm lines around the pin. This will ensure that you're sewing the thread where your point of contact is located on your hands. Sew these lines several times. When you finish doing this, you should have formed a sort of rectangle with the thread. See the images as a reference.
Continue these steps for the rest of the wiring. When you make the first stitch on the edge of the hand for each hand, gently put the gloves on and make sure these stitches touch the point of contact areas on your hands. This is very important because if your stitches don't touch, the LEDs won't light up.