Abstract: A method and apparatus for data compression of input ECG beats in an electro-cardiograph system. The data compression method includes the steps of conditioning the analog input ECG beats into filtered digital data; identifying the individual QRS peaks in the beats; and compressing the beats. The step of compressing a beat includes selectively sub-sampling the beat; template matching and differencing the beat with a template beat, namely the immediately preceding beat of its type (normal, ectopic or artifact); and coding the sub-sampled differenced beat. The step of selective sub-sampling includes dividing the QRS region into at least two sub-regions centered about the QRS peak; and selectively sub-sampling each sub-region at a different compression ratio.