To examine the value of stress and redistribution thallium-201 single photon emission computed tomography (SPECT) for predicting improvement after coronary artery bypass grafting (CABG) and for assessing graft patency, 17 patients underwent SPECT before and after CABG. Preoperatively, 16 patients (94%) showed reversible ischemia with redistribution, and defect score decreased from 16.4 +/- 7.6 to 8.3 +/- 5.8 (p less than 0.001) on 2 hour delayed images. Stress electrocardiography was positive in 15 cases (88%). The stress defect score was reduced postoperatively (7.8 +/- 6.3) as compared to the preoperative score (16.4 +/- 7.6) (p less than 0.001). Postoperatively, 7 cases (41%) showed reversible ischemia and the defect score decreased from 11.3 +/- 6.5 to 6.1 +/- 4.7 (p less than 0.05), while 4 cases (23.5%) showed positive stress electrocardiograms (ECG). Resting left ventricular (LV) ejection fraction (EF) improved in 6 cases (48.3 +/- 5.4% preoperatively to 56.8 +/- 7.4% postoperatively, p less than 0.05) and showed a reduction in 11 (58.2 +/- 10.5% to 47.5 +/- 9.4%, p less than 0.01). Grafts were occluded in 6 cases, and redistribution was evident on the delayed thallium images in all cases (100%), while stress ECG was positive in only 3 (50%). Thus, stress and redistribution SPECT is valuable for identifying patients who will improve after surgery and assessing graft patency more accurately than stress ECG. Resting LVEF was less useful for assessing improvement in LV function.