Abstract Previous studies have revealed that the sympathetic nervous system is more vulnerable to ischemia than the myocardium itself. Thus our study was undertaken to detect denervated myocardium in non-Q-wave myocardial infarction (MI) and unstable angina with iodine 123 metaiodobenzylguanidine ( 123I-MIBG), which can delineate myocardial sympathetic innervation. Eight patients with non-Q-wave MI and 12 with unstable angina were studied. Sequential 123I-MIBG and thallium-201 chloride ( 201TICI) imaging and single-photon emission computed tomography (SPECT) were performed at rest 24 ± 12 days after the last ischemic attack. Myocardial perfusion defect was not detected by 201TICI in 4 of 8 patients with non-Q-wave MI, whereas 123I-MIBG SPECT imaging revealed defects corresponding to myocardial ischemic areas predicted by coronary angiography in all 8 patients. 123I-MIBG imaging revealed defects in 7 of 12 patients with unstable angina corresponding to coronary angiographic findings, whereas no myocardial perfusion defect was detected by 201TICI imaging in any of them. In conclusion, 123I-MIBG SPECT is a sensitive method for detecting myocardium exposed to transient ischemia that cannot be detected by 201TICI imaging.