If you're interested in monitoring the electrical activity of someone's heart over a period of time, or creating a form of lie detector, then this simple project by Will Forfang may be of interest. He describes a method of using real ECG electrodes with an Arduino, which involves constructing an instrumentation amplifier circuit with an op-amp for more gain, that feeds the signal into an Arduino.
The data is then send from the Arduino to an Android device (such as the phone shown below) running a custom app written by the author. This acts as the display device and looks quite professional.
For more details and notes to make your own, check out Will's website. Please note that you shouldn't rely on home-made medical sensors for medical diagnosis (see a Doctor instead). And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.