An active medical device comprising: - an implantable cardiac generator for myocardial stimulation, defibrillation and/or resynchronization, the generator comprising: • at least two detection/stimulation terminals, with a first terminal and a second terminal; • a stimulation circuit suitable for generating electrical stimulation pulses; • a control circuit suitable for controlling delivery, at least at the first terminal, of the pulses generated by the stimulation circuit, and for controlling sequencing of said pulses; and • a collection circuit for collecting an endocardial electrogram signal and for detecting a spontaneous or stimulated cardiac depolarization wave at each cardiac cycle; in which active medical device: - the device further comprises at least one lead (12, 12', 12") for vagus nerve stimulation, which lead is suitable for being implanted on or in the vicinity of the vagus nerve; - the VNS lead (12, 12', 12") is provided with connection means adapted to a cardiac generator; - the VNS lead (12, 12', 12") is connected to the first terminal of the cardiac generator in such a manner as to receive the pulses produced at said terminal by the cardiac generator in order to apply said pulses to the vagus nerve; - the control circuit (30, 40) of the cardiac generator is suitable for controlling the stimulation circuit in such a manner as to produce bursts (Si) of pulses, said bursts being VNS bursts that are generated continuously in succession for periods of activity (T ON) separated by interspersed periods of inactivity (T OFF), and/or that are generated synchronously with detection of a cardiac depolarization wave (R/V); said active medical device being characterized in that: - the control circuit (30, 40) is also suitable for measuring the impedance of the VNS lead, and for responding by dynamically controlling the pulse voltage (V 0) generated by the stimulation circuit in such a manner as to adjust the charge delivered by each stimulation pulse to a value that is constant from one pulse to the next, and from one burst (Si) to the next. - an implantable cardiac generator for myocardial stimulation, defibrillation and/or resynchronization, the generator comprising: • at least two detection/stimulation terminals, with a first terminal and a second terminal; • a stimulation circuit suitable for generating electrical stimulation pulses; • a control circuit suitable for controlling delivery, at least at the first terminal, of the pulses generated by the stimulation circuit, and for controlling sequencing of said pulses; and • a collection circuit for collecting an endocardial electrogram signal and for detecting a spontaneous or stimulated cardiac depolarization wave at each cardiac cycle; • at least two detection/stimulation terminals, with a first terminal and a second terminal; • a stimulation circuit suitable for generating electrical stimulation pulses; • a control circuit suitable for controlling delivery, at least at the first terminal, of the pulses generated by the stimulation circuit, and for controlling sequencing of said pulses; and • a collection circuit for collecting an endocardial electrogram signal and for detecting a spontaneous or stimulated cardiac depolarization wave at each cardiac cycle; - the device further comprises at least one lead (12, 12', 12") for vagus nerve stimulation, which lead is suitable for being implanted on or in the vicinity of the vagus nerve; - the VNS lead (12, 12', 12") is provided with connection means adapted to a cardiac generator; - the VNS lead (12, 12', 12") is connected to the first terminal of the cardiac generator in such a manner as to receive the pulses produced at said terminal by the cardiac generator in order to apply said pulses to the vagus nerve; - the control circuit (30, 40) of the cardiac generator is suitable for controlling the stimulation circuit in such a manner as to produce bursts (Si) of pulses, said bursts being VNS bursts that are generated continuously in succession for periods of activity (T ON) separated by interspersed periods of inactivity (T OFF), and/or that are generated synchronously with detection of a cardiac depolarization wave (R/V); - the control circuit (30, 40) is also suitable for measuring the impedance of the VNS lead, and for responding by dynamically controlling the pulse voltage (V 0) generated by the stimulation circuit in such a manner as to adjust the charge delivered by each stimulation pulse to a value that is constant from one pulse to the next, and from one burst (Si) to the next.