The ability to map and ablate the sometimes fleeting automatic atrial tachycardia is greatly enhanced by computerized mapping systems. In this study, we have developed 128 channel computerized data analysis system using microcomputer for basic research of electrophysiology and electrical propagation. The bipolar electrogram information is acquired from 128 cardiac sites simultaneously at a sampling rate of 1 ksampls/sec with continuous and total data storage of up to 30 seconds. When the reference electrogram is selected and reference point is picked up, delay time from the reference point is displayed on three dimensional diagram of the heart. System design permits easy expansion to almost 256 simul- taneous sites. This system is expected to enable us to study pathophysiology of cardiac arrhythmia and to improve the result of diagnosis and surgical treatment for cardiac arrhythmia.