Well actually they do. Automatic External Defibrillators (AEDs) are designed to work on patients that have an electrical cardiac conditions of V-Tach (with or without pulse- the heart can be beating so fast or uncontrolled, that the chambers of the heart do not refill properly, thus there is no effective output) and V-Fib (the cardiac cells are firing without any type of coordination, to the point where the heart is just quivering). If you mean they will not work on asystole (no electrical activity), then yes, you are correct. Generally, as an area of the heart becomes deprived of oxygen, the normal electrical patterns become erratic, leading to dysrhythmias, of which V-Tach and V-fib are likely. As the heart continues to be starved of oxygen, the electrical activity and pathways become inactive or asystolic. The goal of an AED is not to provide an eternal source of electricity (external pacing does), but to reset the coordinated electrical flow though the heart.

Pete