The relation between the presence of viable myocardium by rest-redistribution thallium imaging and prognosis is not well defined. This study examined the prognostic value of rest-redistribution single-photon emission computed tomographic imaging with thallium-201 in patients with coronary artery disease (CAD) and left ventricular (LV) dysfunction. Patients were divided into 2 groups: group 1 patients (n = 47) were treated medically and group 2 patients (n = 38) underwent coronary revascularization. The 2 groups were comparable in the extent of CAD and in LV ejection fraction. Thallium images showed normal tracer uptake in 1 group 1 and 3 group 2 patients, fixed defects in 26 group 1 and 18 group 2 patients, and both reversible and fixed defects in 20 group 1 and 17 group 2 patients (p = NS). Based on analysis of 20 segments/patient, reversible defects were seen in 4 ± 4 segments/patient in group 1 and 5 ± 5 segments/patient in group 2 (p = NS). Viable myocardium (defined as normal tracer uptake, reversible defects, or mild fixed defects) was seen in 14 ± 4 segments/patient in group 1 and 15 ± 5 segments/ patient in group 2 (p = NS). During a mean follow-up of 31 months, there were 16 group 1 (34%) and 6 group 2 (16%) deaths. The annual mortality rate was 13% in group 1 and 6% in group 2. Actuarial survival analysis showed better survival in group 2 than in group 1 (p = 0.056). Thus, viable myocardium in patients with CAD and LV dysfunction is associated with poor prognosis with medical therapy. Coronary revascularization improves prognosis. © 1995.