Cardiac pacemaker circuit with variable operation

An artificial cardiac pacemaker circuit producing heart stimulation pulses and arranged to operate in any selected one of a plurality of operating modes, the paths traversed by signals in the circuit being different in each operating mode, the circuit including a stage emitting pulses having a predetermined duration and amplitude and/or repetition rate, a stage arranged to actuate further signals during at least a first operating mode in response to such pulses, and a stage operative only during a second operating mode to actuate or suppress such signals at the end, or for the duration, of each pulse in order to at least indirectly fix the time position of each stimulation pulse.