An active implantable medical device provides atrial stimulation for resynchronization of the heart chambers. After a first cycle without stimulation, a premature left atrial stimulation is delivered with application of a short left inter-atrial delay, shorter than the sinus rhythm coupling interval. During the next cycle a non-premature left atrial stimulation is delivered, and the atrioventricular interval between the left atrial depolarization and the ventricular depolarization is evaluated and compared to its value in sinus rhythm to modify as necessary a parameter of the left atrial stimulation, such as the short left inter-atrial delay.
