An implantable pulse generator (IPG) with a cardiac rhythm recognition system, to analyse an electrocardiogram (ECG), intended to deliver an electrical impulse(s) to defibrillate the heart (restore normal rhythm) or slow a rapid heart rate, and typically to pace a slow heart rate. It is implanted in a pouch beneath the skin of the patient's chest or abdomen and has connected a lead(s) that are positioned inside or on one heart chamber (typically right ventricle) to monitor the ECG and to automatically deliver the electrical impulse. It has internal batteries that provide the energy for the discharges; it is commonly known as an automatic implantable cardioverter-defibrillator (AICD).