Scott Harden has a great section on his blog about his DIY ECG and heart rate analysis. He lets the software GoldWave clean up the noise in the signal and uses nonshielded electrodes.
"The openECGproject is an online community conceived around a simple, but challenging and worthy goal - to develop an open source hardware and software solution for electrocardiography .
This is essentially a playground designed for people of different backgrounds to put their minds together and create something that could make a difference in this world. It started as an itch that needed scratching, so Dr. Ivor Kovic initiated this community with high hopes that people who can make this vision come true will join and contribute to the project. Read more about the people behind the openECGproject."
Image from Gray's Anatomy