Patients with idiopathic dilated cardiomyopathy (IDC) constitute a minority among implantable cardioverter-defibrillator (ICD) recipients; how these patients fare versus those with coronary artery disease (CAD) is not well defined, nor is the mechanism of cardiac arrest recurrence, which may involve a more significant role of bradyarrhythmias. A retrospective multicenter study regarding outcome of ICD therapy was conducted in 224 patients with either IDC (n = 69; 31%) or CAD (n = 155; 69%) presenting exclusively with ventricular fibrillation (VF) unassociated with acute myocardial infarction. Patients with IDC were significantly younger (mean age 57 vs 61 years in patients with CAD, p < 0.04) and less male predominant (64 vs 79% in patients with CAD, p < 0.02). There was no significant difference in mean left ventricular ejection fraction (0.27 in IDC patients vs 0.29 in CAD patients), but sustained ventricular tachycardia was induced less often in patients with IDC (21 vs 58% in CAD patients, p < 0.001). Bradycardia pacing, either by an ICD with bradycardia pacing ability or a separate bradycardia pacemaker, was available in only 15% of ICD implantees. During a median follow-up duration of 1.7 years for patients with IDC and 1.9 years for patients with CAD, estimated cumulative event rates were similar for any type shock (2-year incidence of 74% in IDC patients, 69% in CAD patients) as well as for appropriate shock (2-year incidence of 46% in IDC patients, 40% in CAD patients).(ABSTRACT TRUNCATED AT 250 WORDS)