Electrocardiography is the recording of the electrical activity of the heart. Traditionally this is in the form of a transthoracic (across the thorax or chest) interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the surface of the skin and recorded or displayed by a device external to the body. The recording produced by this noninvasive procedure is termed an electrocardiogram (also ECG or EKG).
[source: http://en.wikipedia.org/wiki/Electrocardiography ]
In 1902, Einthoven published the first ECG recorded on a string galvanometer. This instrument used a thin, silver-coated, quartz string stretched across a magnetic field. The heart’s electrical current caused the string to move from side to side, which could be recorded photographically.
Einthoven’s early machine weighed 600 pounds and required five people to operate it. It was located in his lab at Leiden University in the Netherlands. By using a telephone cable, Einthoven was later able to transmit ECGs from patients in the hospital to the lab. In the next few years, several hospitals set up “electrocardiographic stations.” Smaller machines were soon developed, and in 1909, the first string galvanometer was installed in the US.
I am planning to build an electrocardiograph using AD620 ICs, home-made electrodes and modified CRT as a display.