Ole Andreas Utstumo designed this board to log ECG waveforms:
Heartbeat Logger
A portable device that will log your ECG – the “waveform” of your heart – to your phone via bluetooth or to a memory card
The Heartbeat Logger is a portable device that that logs your ECG throughout the day and throughout the night, 24/7. While this certainly is nothing new, even as an open source project (see MobilECG), Heartbeat is a project that, aside being of personal value for me, is designed to be simple to use and understand, and might serve a purpose somewhere for someone.
The firmware and hardware design is available on GitHub:
OSH Park 