Noninvasive detection of restenosis in patients remaining asymptomatic after percutaneous transluminal coronary angioplasty (PTCA) remains a major clinical problem. The value of exercise electrocardiography (ECG) and exercise-redistribution thallium-201 single-photon emission computed tomography (SPECT) in detecting restenosis in such patients remains uncertain. Discordances between these tests and coronary angiography is a common situation. We studied 179 consecutive patients remaining asymptomatic after successful PTCA (208 vessels), who underwent 6 +/- 2 months of exercise ECG, SPECT, and coronary angiography. We sought to assess the diagnostic value of the noninvasive tests compared with coronary angiography, and identify the determinants of discordances between the tests. Restenosis (diameter stenosis >50%) was detected in 39% of patients and in 37% of vessels. The overall sensitivity, specificity, and accuracy for exercise ECG and SPECT in detecting restenosis in individual vessels were, respectively, 53% versus 63% (p = 0.06), 59% versus 77% (p = 0.0001), and 57% versus 72% (p = 0. 0001). On multivariate analysis, positive exercise ECG was associated with higher heart rate response (p = 0.02), incomplete revascularization (p = 0.004), and angiographic restenosis (p = 0. 03), whereas positive SPECT was associated with incomplete revascularization (p = 0.02), infarct-related artery PTCA (p = 0.01), and angiographic restenosis (p = 0.0001). Accuracies of the 2 tests were not significantly different in patients with incomplete revascularization or PTCA of an infarct-related vessel. Overall, SPECT is more accurate than exercise ECG in detecting asymptomatic restenosis. Nevertheless, incomplete revascularization and PTCA of an infarct-related artery could cause reversible perfusion defects regardless of restenosis, reducing the diagnostic value of SPECT in such patients.