The Hewlett-Packard ECG Diagnostic Program was evaluated in a sample of 1000 ECGs. Program accuracy was judged, using a cardiologist as ″gold standard″ . The usefulness of the criteria adjustment feature was evaluated by analyzing a subset of 500 ECGs before and after criteria adjustment. Program sensitivity, specificity and predictive accuracy were 91%, 99. 1% and 91. 9%, respectively. When clinically relevant information only was considered, the respective figures were 96. 5%, 99. 5% and 95. 3%. After criteria adjustment, there was improvement in overall ECG and severity level agreement. There were also small but definite improvements in sensitivity and predictive accuracy after criteria adjustment. Approximately 95% of rhythms were diagnosed correctly.