An active implantable medical device of the cardiac stimulation, resynchronization and/or defibrillation prosthesis type, the device comprising: - a first stimulation/detection electrode to be implanted at the right atrium; - a second stimulation/detection electrode to be implanted at the left atrium; - a generator capable of ensuring: - the delivery of left atrium stimulation pulses (StimOG) by said second stimulation/detection electrode; and - selectively based on adjustable control parameters, the premature delivery of said left atrium stimulation pulses, while applying a shortened inter-atrial coupling that is shorter than the sinus rhythm coupling interval, characterized in that the device is deprived of means for collecting and analyzing the endocardial acceleration, and in that it comprises a digital processor configured to control the generator in such a manner that: - after a first cardiac cycle without left atrium stimulation (Cyle 2), a left atrium stimulation pulse is delivered during an immediately subsequent second cardiac cycle (Cycle 3), while applying a first inter-atrial coupling, said first inter-atrial coupling applied during the immediately subsequent second cardiac cycle being a shortened coupling, that is shorter than the sinus rhythm coupling interval, in order for said left atrium stimulation pulse delivered during this second cardiac cycle to be a premature pulse; - a non premature left atrium stimulation pulse is delivered during a third cardiac cycle (Cycle 4) that is immediately subsequent to said second cardiac cycle (Cycle 3), while applying a second inter-atrial coupling corresponding to the sinus rhythm coupling interval, and in that the digital processor is configured so as to: • evaluate the right atrial coupling interval separating the right atrial depolarizations in said second and third cardiac cycles; • compare the right atrial coupling interval thus evaluated with the sinus rhythm coupling interval; and • modify or not at least one of said adjustable control parameters according to the result of the comparison. - a first stimulation/detection electrode to be implanted at the right atrium; - a second stimulation/detection electrode to be implanted at the left atrium; - a generator capable of ensuring: - the delivery of left atrium stimulation pulses (StimOG) by said second stimulation/detection electrode; and - selectively based on adjustable control parameters, the premature delivery of said left atrium stimulation pulses, while applying a shortened inter-atrial coupling that is shorter than the sinus rhythm coupling interval, - the delivery of left atrium stimulation pulses (StimOG) by said second stimulation/detection electrode; and - selectively based on adjustable control parameters, the premature delivery of said left atrium stimulation pulses, while applying a shortened inter-atrial coupling that is shorter than the sinus rhythm coupling interval, - after a first cardiac cycle without left atrium stimulation (Cyle 2), a left atrium stimulation pulse is delivered during an immediately subsequent second cardiac cycle (Cycle 3), while applying a first inter-atrial coupling, said first inter-atrial coupling applied during the immediately subsequent second cardiac cycle being a shortened coupling, that is shorter than the sinus rhythm coupling interval, in order for said left atrium stimulation pulse delivered during this second cardiac cycle to be a premature pulse; - a non premature left atrium stimulation pulse is delivered during a third cardiac cycle (Cycle 4) that is immediately subsequent to said second cardiac cycle (Cycle 3), while applying a second inter-atrial coupling corresponding to the sinus rhythm coupling interval, • evaluate the right atrial coupling interval separating the right atrial depolarizations in said second and third cardiac cycles; • compare the right atrial coupling interval thus evaluated with the sinus rhythm coupling interval; and • modify or not at least one of said adjustable control parameters according to the result of the comparison.