The present invention relates to a device for generating a defibrillation shock, characterized in that, the device is a portable automated external defibrillator comprising a positive electrode attachable to a subjects body for allowing electrical current to flow from the device to the subjects body; a negative electrode attachable to another area of the subjects body for allowing electrical current to flow from the subjects body to the device; a sensing unit for recording electrical activity data of the subjects heart; an electrical power supply unit for supplying electricity to the device; a high voltage electrical supply unit for supplying a high voltage electricity to the subjects body; an input unit for generating an input signal; an output unit for generating an information for a user; a controlling unit, wherein the controlling unit process, send and retrieve data and signals between the sensing unit, the high voltage electric supply unit, the input unit, and the output unit; a switching system for allowing, preventing and regulating electrical current to flow from the high voltage electrical supply unit to the positive electrode and from the negative electrode to the sensing unit; and a housing structure for housing the sensing unit, the electrical power supply unit, the high voltage electrical supply unit, the input unit, the output unit, the controlling unit, and the switching system. The portable automated external defibrillator is compact and easy to carry.