The present disclosure relates to an implantable medical device, in particular cardiac defibrillator, comprising an implantable defibrillator configured to generate an electrical defibrillation signal； an implantable electrode connected with the implantable defibrillator by a lead and configured to deliver the electrical defibrillation signal to a patient； an implantable sensor means configured to detect mechanical vibrations by the heart of the patient and to provide a detection signal based on the detected mechanical vibrations； and a controller configured to analyze the detection signal to determine at least one parameter characterizing the mechanical vibrations and to initiate a defibrillation operation of the implantable defibrillator or not based on the determined parameter characterizing the mechanical vibrations only.
