BACKGROUND AND OBJECTIVE: Ventricular arrhythmia is an important cause of death in patients suffering with idiopathic dilated cardiomyopathy (IDCM). The decreased uptake or increased "washout" of 123I-metaiodobenzylguanidine (MIBG)-derived radioactivity is associated with a worse prognosis or severe disease in patients with cardiac diseases. SUBJECTS AND METHODS: Forty patients (28 men, mean age: 56.5+/-13.0 years) with angiographically proven IDCM were studied and divided into 2 groups: the patients with clinically documented ventricular tachycardia (VT) and IDCM (group A; 17 patients), and the patients without VT, but with IDCM (group B; 23 patients). The normal control group (7 men, mean age 62.4+/-7.9) was compared theses patients. 123I-MIBG was evaluated by the early (15 min) and delayed (3hours) uptake, the heart to mediastinum uptake (H/M) ratio and the global and regional washout ratio (WOR) that was defined as the [early H uptake-delayed H uptake]/early H uptake. The clinical variables, echocardiographic parameters and 123I-MIBG-derived parameters were compared among three groups. RESULTS: There were no significant differences in age and the echocardiographic parameters between the groups A and B. A significant negative correlation was present between the early inferior wall H/M ratio and the LVEDD (Spearman's correlation, r=-0.412, p=0.08), and the early inferior H/M ratio and the LVESD (Spearman's correlation, r=-0.463, p=0.03). Only the delayed lateral wall uptake was significantly lower in group A than that in group B (23.3+/-5.3 versus 27.8+/-8.4, respectively p=0.042). The regional WOR was not statically different among the three groups. CONCLUSION: Cardiac 123I-MIBG SPECT partially reflects the vulnerability for the occurrence of VT in patients suffering with IDCM. These results support the feasibility of using cardiac 123I-MIBG SPECT as a prognostic tool in IDCM patients.