Abstract: A method and apparatus for an ambulatory electrocardiographic monitoring system for recording, detection, measurement, analysis and plotting of high resolution electrocardiographic data having a modified Holter recorder that performs digital signal averaging of selected signals as well as storing for future playback all ECG beats. The digitally signal averaged beats are correlated with a previously defined correlation coefficient yielding summated results that have eliminated nonrepetitive noise to less than a microvolt. By real time averaging approximately 1000 beats during a 10 to 15 minute period and digitally storing the averaged data, micropotential averaging can be performed several times per hour for up to 24-hours. Analog recordings are precalibrated for accurate amplitude representation as well as providing an option for standard one millivolt calibration pulses at the beginning of the tape.