Building ECG monitoring device is a bit challenging as you have to deal with noisy low voltage signals. Probably most important part in all this is analog signal amplification and filtering circuit. So here is a nice compact DIY ECG monitoring device built around Parallax Propeller microcontroller.
It’s a single channel ECG circuit that captures electrical signals from body when thumbs are placed on PCB pads that are located on edge of board. Then signal is amplified with instrumental amplifier AD627 and then again with dual op-amp TC1029. Then signal is passed through low pass filter before enters microcontroller ADC input. There is a LED on board that indicates detected heart beat. And of course the USART link to PC software that allows viewing ECG waveform. Of course this project is amateur so don’t use it as reference when medical problems occur. And as warning states – always make sure there is no risk of electric shock when exposing electronics to your body.