Implanted electronic medical devices. or stimulators such as pacemakers and nerve stimulators have grown enormously in diversity and complexity over recent decades. The function and potential interaction of these devices with the perioperative environment is of increasing concern for anesthesiologists and surgeons. Because of the innate electromagnetic environment of the hospital (operating room, gastrointestinal procedure suite, and imaging suite), implanted device malfunction, reprogramming, or destruction may occur and cause physical harm (including nerve injury, blindness, deafness, burn, stroke, paralysis, or coma) to the patient. It is critical for the anesthesiologist and surgeon to be aware of the function and interaction of implanted devices, both with other implanted devices and procedures (such as magnetic resonance imaging and cardioversion) in the hospital environment. Because of these interactions, it is imperative that proper device function is assessed when the surgical procedure is complete. This review article will discuss these important issues for 12 different types of "little black boxes," or noncardiac implantable electronic medical devices.