Active implantable medical device, in particular pacemaker, defibrillator and / or cardioverter type ddd / aai has optimized operation effort has

This device comprises means for sensing spontaneous atrial and ventricular events, means for detecting the presence or absence of a spontaneous atrioventricular conduction, and means for ventricular and atrial stimulation. It further comprises means such as an activity sensor for discriminating (12, 42) between phases of effort and rest, means for measuring the atrio-ventricular conduction time separating an atrial event, spontaneous or stimulated, of a spontaneous ventricular event following corresponding means (14, 32) of diagnostic good or bad adaptation of conduction time to stress, said means operating by evaluating, during exercise, of the variation of the conduction time depending on the variation of the frequency. It may also be provided means (40) adapted, when the diagnosis means indicates a bad adaptation to effort, to deactivate the automatic switching mode, to switch the device to DDD mode and to reprogram the atrio-ventricular delay to a shorter than the previously programmed value value.