Dipyridamole thallium imaging is one of the most widely accepted means of evaluating patients with suspected or known coronay artery disease. The results of thallium imaging help diagnose coronary artery disesse (CAD), determine the hemodynamic significance of coronary stenosis, evaluate viability of myocardium, assess the outcome of therapeutic interventions and stratify patients according t.o their risk for futher cardiac events. An increased lung thallium uptake and transient LV dilation has been reported as poor prognostic indicator and associated with extensive and severe coronary artery disease. We quantitated lung/heart uptake ratio (L/HUR) and transient left ventricular dilation ratio in 44 patients and 17 controls undertaking dipyridamole thalliurn-201 scintigraphy. The results are as follows: 1) The lung/heart uptake ratio was high in patients with CAD and which became higher according to increasing number of diseased vessel, The L/HUR of patients with low LVEP (<35%) was lower than those with normal LVEF. 2) Transient left ventricular dilation ratio of CAD patients had no close relation between numbers of diseased vessels and was not highqr than normals. But transient left ventricular dilation ratio of patients with myocardial infartion was higher than normals. We concluded that lung/heart uptake ratio seems to be sensitive marker for severity of CAD and myocardial function, but transient left ventricular dilation ratio alone is not sufficient to be a marker for severe and extensive CAD.