Coronary atherosclerosis often presents as sudden death or myocardial infarction after a clinically silent period of advanced anatomic disease. Since atherosclerosis appears to be reversible a routine non-invasive screening test for the reliable diagnosis of mild coronary lesions would permit potential selective prevention of these sequelae by intensive dietary management, drug therapy and physical training with the regression or progression of the lesions being followed by repeated tests. If widely accessible, such a test could have a profound impact on current approaches to the treatment of coronary disease. Although Thallium-201 myocardial imaging has been an important development in the non-invasive diagnosis of coronary stenoses, it gives falsely negative results in 19% to 39% of patients with arteriographically significant coronary lesions. It is therefore of limited value as a screening procedure, particularly when applied to an asymptomatic population in which the prevalence of disease is less than 15%. Over the past four years the principal investigator has developed the physiologic basis of a non-invasive technique for detecting 40% diameter stenoses of coronary arteries by cross sectional tomographic myocardial imaging of regional and epicardial-endocardial perfusion during maximal pharmacologic coronary vasodilation. The method requires: (a) a potent stimulus for coronary vasodilation, such as intervenous dipyridamole, which maximizes regional perfusion abnormalities without producing myocardial ischemia as a diagnostic end point, is not affected by patient motivation, pulmonary or peripheral vascular disease, as in treadmill testing and can be controlled by dose adjustment and intravenous aminophylline, an instantaneous antagonist of dipyridamole, (b) an imaging agent taken up by the myocardium in proportion to coronary flow at flow rates up to 5 times resting coronary flow so that diferences in regional maximum flows caused by mild stenoses can be identified and (c) cross sectional tomographic myocardial imaging in order to visualize relative endocardial-epicardial perfusion, the most sensitive indication of the hemodynamic effects of coronary stenoses, and in order to exclude form the imaging field the interfering activity of lung, background and overlying heart structures. The purpose of this project is to apply these three principles to clinical myocardial imaging in order to develop a non-invasive s (Text Truncated - Exceeds Capacity)