In 1988, coronary heart disease was the leading cause of death in the United States, accounting for some 500,000 lives annually. The search continued for non-invasive ways of improving risk-detection in the population prior to and after manifest disease. Detection of silent ischemia, as indicated by the presence of asymptomatic intermittent ST depression detected by ECG monitoring, was accomplished by non-invasive means and data analysis was determined with current, automated analysis programs. However, there were insufficient data to assign definite prognostic import to intermittent STD. The studies addressing this question were in selected populations and yielded conflicting results. This was in part due to the small size of the populations previously studied. The size of this study's population permitted examination of additional criteria for ST changes in relation to prognosis. A finding that transient ischemia adversely affected prognosis in a large group of patients who had myocardial infarction would therefore give confidence to the medical community in an accessible non-invasive technique to identify those at highest risk. This would have an important impact on patient management. Impetus would also be given toward studying asymptomatic STD among high risk patients (hypertensives, hypercholesterolemics, smokers, and diabetics) without clinical coronary heart disease to determine if its presence increased the risk of developing myocardial infarction or sudden death.