Abstract: A computer controls a video display having a display screen for displaying ECG heartbeats superimposed over one another. The ECG data is collected during Holter monitoring and stored in a memory. The Holter monitor preliminarily classifies each beat to a morphology. A representative sample of each morphology is presented in a display window. Each sample can be overlaid with any other selected sample, in different colors, in a compare window having an enlarged scale from the display windows. After comparison, different morphologies can be merged and a selected beat classification can be reclassified to another morphology.