Electrodes can generate electrical stimulation pulses at least one first intensity level and at least one second intensity level. The first and second intensity levels are above and below a given stimulation threshold, respectively. The synchronous or asynchronous delivery of second-level pulses enables the conduction of the atrioventricular node to be modulated by electrotonic effect, for example, to reduce ventricular frequency in the event of atrial fibrillation.