BACKGROUND Patients with congenital left ventricular aneurysms and diverticula may present with arrhythmia. The incidence of ventricular arrhythmias and the clinical outcome of these patients has not been reported to date. METHODS Among 250 consecutive patients with congenital left ventricular aneurysms and diverticula detected by echocardiography, the clinical outcome of patients who presented with ventricular arrhythmias or associated symptoms was investigated. RESULTS 30 out of 250 patients with congenital left ventricular aneurysms and diverticula had ventricular arrhythmias or syncope at initial presentation. During a follow-up of 85 months, spontaneous ventricular tachycardia occurred in 17 of these patients (57%). ventricular tachycardia were sustained in 13, with a monomorphic pattern in 9 patients. In 82% (11 patients) ventricular tachycardia was inducible during electrophysiologic testing. In 7 patients a sustained monomorphic ventricular tachycardia with a right bundle branch block pattern similar to the clinical tachycardia was induced. 20 patients were treated with antiarrhythmic agents. 11 patients received an implantable cardioverter defibrillator. Appropriate device discharges were observed in 73% during a follow-up of 61 months. One patient underwent surgical resection of a congenital left ventricular aneurysm. Three patients underwent successful catheter ablation for incessant ventricular tachycardia. Two of them were free of any clinically relevant arrhythmia during follow-up. Three patients died (10, 41 and 89 months after initial presentation). In two of them, the cause of death was attributed to ventricular arrhythmia. CONCLUSION The clinical outcome of patients with congenital left ventricular aneurysms and diverticula and arrhythmia is variable. Clinical ventricular tachycardia in these patients are often monomorphic and usually inducible during electrophysiologic study, indicating a role for this test in risk stratification. Appropriate discharges are frequent in implantable cardioverter defibrillator recipients with congenital left ventricular aneurysms and diverticula.