An active implantable medical device having a function for monitoring the sympathico-vagal activity by an analysis of endocardiac acceleration. The device collects at least one physiological parameter of the patient, analyzes that collected parameter and delivers at an output data representative of the sympathico-vagal activity of the patient. The physiological parameter is an endocardiac acceleration (EA), and the representative data include at least one value function of the endocardiac acceleration, in particular a function of a first peak (PEA I) at the time of the phase of isovolumic ventricular contraction and/or of a second peak (PEA II) at the time of the phase of isovolumic ventricular relieving.