The electric field of the heart was described diagrammatically for the first time by A. Waller in 1888. However, it was not until a little more than ten years ago that with the development of micro electronic techniques, it became accessible to biophysical modeling, to exact physiological measurements, and to application in advanced clinical diagnosis. These possibilities opened the way to the treatment of questions which are called the direct and the inverse solution of the cardioelectric problem. Several groups of investigators are now working to achieve a complete biophysical and...