by Forrest Sheng Bao http://fsbao.net
Below is a real ECG sampled from me! You can see the signal is highly polluted by 60Hz noise from our power system (60Hz in North America and 50Hz in elsewhere.) There are exactly 6 peaks of the same amplitude in 0.1 second. So, my ECG is modulated on a 60Hz base band signal. you can imagine my ECG by drawing a line from the middle of the 60Hz wave.
I have also moved the circuit to a PCB prototyping matrix board. I used the analog I/O and power supply on NI ELVIS to test it with a simulated ECG signal. Wunderbarschon!