['To assess the prognostic value of cardiac iodine-123 metaiodobenzylguanidine ((123)I-MIBG) scintigraphy to predict ventricular arrhythmias in patients with heart failure (HF) listed for implantable cardioverter-defibrillator (ICD) devices as primary prevention.', 'A prospective cohort study in 27 patients with HF referred for ICD implantation (alone or in combination with cardiac resynchronisation therapy) at a tertiary cardiac centre.', 'Cardiac (123)I-MIBG scintigraphy was performed with calculation of early and late heart-to-mediastinum (H:M) ratios, washout rate, and summed defect score from single photon emission computed tomography (SPECT) acquisition. Resting myocardial perfusion SPECT using (99m)Tc-tetrofosmin was also performed and a summed score calculated. Innervation-perfusion mismatch was evaluated by comparing SPECT scores.', 'Ventricular arrhythmia requiring ICD therapy.', 'At 16 months median follow-up, 10 (37%) patients experienced a significant arrhythmic event. Compared with patients who suffered no event, these individuals had lower early and late H:M ratio and higher (123)I-MIBG SPECT defect scores: 1.83 ± 0.43 versus 2.34 ± 0.33 (p<0.001); 1.54 ± 0.38 versus 1.96 ± 0.38 (p=0.005); 37.0 ± 9.4 versus 25.5 ± 7.7 (p=0.001). Mismatch scores were also higher: 18.5 ± 8.5 versus 8.4 ± 5.0 (p<0.01). Optimal thresholds for predicting arrhythmia were <1.94 for early H:M ratio (sensitivity 70%, specificity 88%); <1.54 for late H:M ratio (sensitivity 60%, specificity 88%); (123)I-MIBG SPECT defect score ≥31 (sensitivity 78%, specificity 77%).'] Does cardiac iodine-123 metaiodobenzylguanidine imaging predict ventricular arrhythmia in heart failure patients receiving an implantable cardioverter-defibrillator for primary prevention?