To display the wave I am using XOSCILLO, a very cool and open source tool (which I wrote :P) that converts your Arduino into an oscilloscope.
Circuit diagram
Here is the scheme, I am using the typical instrumental amplifier(ins amp) and then another op amp to get some more gain. An ins-amp is like an op-amps but with a huge CMRR, I am using a AD8221 which comes in a tiny small package, it’s lead pitch is only 0.65mm, if you want to know what I did to create a simple breakout board please follow this link.
I’m using a single supply for the amps that comes from the arduino 5V pin, and I am creating a buffered virtual ground, this is really important.
For more detail: Minimal ECG using an Arduino and Xoscillo