an active implantable medical device having a plurality of connection terminals able to be connected to electrodes placed in at least three distinct respective sites in a myocardium ; circuits for measuring an intracardiac bio - impedance , comprising circuits for injecting a current and circuits for collecting a voltage at respective poles of a configuration of said connection terminals , and circuits able to deliver at an output a dynamic impedance signal that is a function of the injected current and the collected voltage ; and circuits for evaluating an intracardiac volume , receiving at in input the impedance signal and delivering at an output a dynamic value of volume representing an instantaneous absolute value of intracardiac volume .