Serial comparison of electrocardiograms (ECGs) can provide a useful clinical function by reporting to the editing cardiologist the diagnostic changes that have occurred since the previous ECG. This program detects "significant measurement differences" in each of the diagnostic categories to detect these changes. We evaluated the accuracy and use of this serial comparison program by comparing the diagnostic results of the program with those of an expert cardiologist using a database of ECGs obtained from patients with symptoms admitted to the hospital and other laboratory results consistent with acute myocardial infarction. We found that the level of agreement between the computer and the cardiologist was much higher when a current ECG was compared with a previous that had been edited by the cardiologist than when that same ECG was analyzed in isolation.