Sudden cardiac death (SCD) is a major health problem because it is very common, occurs suddenly and unexpectedly, and is often fatal. Epidemiology of SCD is also very uncertain because it is often unwitnessed, cause is difficult to assess, initial rhythm is often unknown, time since onset cannot be certain, and usually the account is based on statement of bystander or rarely on records of emergency medical staff. The idea of putting a device to diagnose and treat cardiac arrest (AICD) met with lots of resistance initially and many thought it was not an ideal solution. Major technical developments in AICD devices, the refinements in the implant procedures and data from the randomized trials pointed to the usefulness of these devises in secondary prevention of SCD.