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[123I]MIBG has been proposed as a suitable tracer of the adrenergic system of the heart. The aims of this study was to investigate the adrenergic functional status of the heart in hypertensive patients with left ventricular hypertrophy (LVH), and to evaluate the distribution of neuroadrenergic terminals in patients with left ventricular aneurysms (LVA) presenting complex arrhythmias. We studied 21 patients (4 normals, 11 with LVH and hypertension, and 6 with previous myocardial infarction, LVA and complex arrhythmias) who underwent series of [123I]MIBG planar scans (from 0.5 to 24 hours p.i.) and SPECT scans using both [123I]MIBG and 201Tl. Data quantification was performed by calculating the heart/mediastinum ratio (planar scan) and the percent uptake in 5 myocardial regions (SPECT scan). No significant differences between normals and hypertensive patients were found either in the heart/mediastinum ratio or in the regional distribution of [123I]MIBG and 201Tl. In hypertensive patients the uptake of [123I]MIBG was significantly higher than that of 201Tl in the septal wall while in the lateral and inferior walls it was significantly lower. In patients with anteroapical myocardial infarction (MI), the size of the [123I]MIBG defect was slightly smaller than the 201Tl defect; moreover a constant, severe [123I]MIBG defect was observed in the inferior walls whereas 201Tl uptake was normal. We conclude that while in hypertensive patients adrenergic innervation seems to be slightly impaired as compared to myocardial perfusion, in patients with MI a large area of functional or anatomical denervation may be detected despite the preserved perfusion and viability; this mismatch may be the trigger of complex arrhythmias.