A few nice heart image images I found:
Hacking the Heart Spark with a proximity sensor - testing on the sillyscope
Image by Rain Rabbit
Hacking Eric Boyd's Heart Spark pendant, which pulses LEDs my heartbeat via my Polar gym chest strap transmitter. I've been experimenting with a proximity sensor to light up the top 3 LEDs on the Heart Spark. It's been very much trial and error to get it to work with various voltage supplies, so far I've tried a 3V coin and a AAA battery with a step up voltage component. It works best as seen in this image with a 4.4V supply from a variable mains adapter.
Image by Robert Hruzek
Special effects sure can make a dramatic image!