Here’s a cool DIY on howto build your own heart rate monitoring device using an Atmel Atmega8
microcontroller. You can probably easily make this idea work with any other microcontroller out
on the market with an ADC.
After a little introduction into ECG we will move on to the electronic description. The simplest way to explain how it works is to make a block diagram! The signal from the body is being amplified(the signals from the body are small and weak, ranging from 0.5 mV to 5.0 mV), filtered (to remove the noise), sampled (by sampling I mean it goes to an Analog to Digital converter aka ADC) and then sent to your computer through RS232 (wireless or any other way but RS232 was chosen because it is the simplest and fastest to make).