The invention relates to an implantable
medical device for stimulating a human or animal heart, the device comprising a
single electrode (20) comprising a proximal
electrode pole (213) designed and arranged to be implanted within an atrium (2) of the heart (1) to be stimulated and a distal
electrode pole (203) designed and arranged to be implanted within a septum (13) of the heart (1) to be stimulated. During operation, the implantable
medical device performs the following steps: a) detecting (500) an intrinsic atrial contraction of the heart (1) to be stimulated with the proximal
electrode pole (213) or stimulating (500) the atrium (2) of the heart (1) to be stimulated with the proximal electrode pole (213); b) detecting (530) an intrinsic
ventricular contraction of the heart (1) to be stimulated with the distal electrode pole (203); c) determining (530) an intrinsic
atrioventricular conduction time between i) the intrinsic atrial contraction or the stimulation of the atrium and ii) the intrinsic
ventricular contraction; d) setting (550) a stimulated
atrioventricular conduction time for stimulating a
ventricle (3, 5) of the heart (1) to be stimulated with the distal electrode pole (203), the stimulated
atrioventricular conduction time being shorter than the intrinsic atrioventricular
conduction time.