RaysLogic has posted his plans for a Parallax Propeller based heart rate monitor. Dubbed the PropEKG, Ray’s design uses an AD627 instrument amplifier and TC1029 dual op amp. Data is processed by the Propeller and relayed to a Windows PC using a Parallax PropPlug (normally used for programming a Propeller chip.) The circuit is isolated from the PC for safety purposes using an H11L opto-isolator.
Ray’s website has the schematic and links to the Propeller code and the associated Windows application.