Primary and secondary prevention of sudden cardiac death is not sufficiently assured by medication. The (automatic) implantable cardioverter/defibrillator ((A)ICD) is able to terminate life-threatening arrhythmias (ventricular fibrillation/flutter, ventricular tachycardia) reliably. The identification and care of risk patients is of crucial importance. Initially, only survived resuscitation for ventricular fibrillation or ventricular tachycardia was regarded as a confirmed indication. Several studies (CABG patch, MADIT, MADIT II, MUSTT, DINAMIT, CAT AMIOVIRT, DEFINITE, COMPANION, SCD-HeFT) have examined the prophylactic indication for ICD therapy in risk groups. Patients with chronic state after myocardial infarction with markedly impaired left ventricular function and/or spontaneous, non-sustained ventricular tachycardia have been documented to benefit. Patients with moderately severe or severe heart failure also profit from ICD implantation, where appropriate in combination with cardiac resynchronization therapy in conduction disorders. There is divergent data on dilated cardiomyopathy. ICD is not indicated in patients with acute infarctions or undergoing elective bypass surgery.