It's amazing what homebrew coders for the PSP are able to come up with, especially when you consider that the "solutions" don't really solve anything. If you've ever hankered for a heartbeat recognition ability for your portable gaming machine, then here it is.
One guy called Art simply soldered a coiled copper wire across the microphone input, which allows it to pick up the signal from a wireless heartbeat sensor. The result isn't visually impressive -- he hasn't coded a graphical readout yet -- but it should definitely inspire confidence in the homebrew community's ingenuity. PSP pull-ups anyone?