The quantitative assessment of infero-posterior defect on 123I-metaiodobenzylguanidine (MIBG) myocardial scintigraphy was studied in 150 patients with non-ischemic heart diseases at rest. The bull's eye map, obtained from the SPECT images at 4 hours after MIBG injection, was evaluated by generating the blacked out map which exhibits regions with reduced % uptake under mean-2 SD of 13 normal controls. The blacked out regions involved infero-posterior segments and were closely resembled to the sector form. The central angle of this sector, which was named as angle of defect (AOD), significantly correlated with both the heart-to-mediastinum activity ratio (H/M) and the myocardial clearance of MIBG. Because H/M and clearance are widely used as quantitative indices in MIBG myocardial scintigraphy, these results indicate that AOD can also be used as a quantitative index of abnormal cardiac sympathetic nervous function, which is likely to appear in infero-posterior regions in non-ischemic cardiac diseases.