Forty patients (38 men and 2 women, mean age 56 +/- 9 years) with angiographic evidence of coronary artery disease underwent 201Thallium myocardial scintigraphy and two-dimensional echocardiography. 201Thallium uptake and echocardiographic regional ventricular function were studied in corresponding myocardial segments. On exercise-redistribution 201Thallium imaging, 308 segments (51% of the total) had normal Thallium uptake, 48 (8%) exhibited reversible defects and 244 (41%) irreversible defects. Of the latter 244 segments with irreversible defects, 114 (47%) exhibited increased tracer uptake (Re+) and 130 (53%) remained unchanged (Re-) after 201Thallium reinjection at rest. Regional ventricular function was significantly better in the segments with normal Thallium uptake than in the segments with reversible or irreversible defects (p < 0.001). Furthermore, the segments with irreversible defects Re- had impaired regional function compared to the segments with irreversible defects Re+ (p < 0.001). Coronary artery stenosis was significantly more severe in the segments with irreversible defects Re- (93 +/- 16%) than in those with reversible defects (81 +/- 20%) and with irreversible Re+ defects (80 +/- 20%) (both p < 0.001). In conclusion, in coronary artery disease patients, exercise-redistribution 201Thallium cardiac imaging with reinjection at rest can identify severely ischemic but still viable myocardium and may be particularly useful in the prognosis of such patients.