The AICD represents a major technologic advance for patients with life-threatening ventricular tachyarrhythmias in whom drug or surgical therapy is unsuccessful. A significant reduction in mortality in these patients is seen with AICD use. As the device becomes more widely available and more centers in the country become adept in its implantation and use, a rapidly expanding patient population with AICDs will exist. These patients, who typically have severe underlying cardiac disease and are at high risk for sudden cardiac death, will present in increasing numbers to EDs with complaints related to the device. Emergency physicians must be prepared to evaluate and treat AICD patients and must be aware of the complications and problems associated with AICDs. This preparation will ensure that the AICD patient will receive prompt and appropriately directed treatment in the ED.