A procedure to operate a hybrid-electric power train and a device to implement the procedure are proposed. The hybrid-electric power train contains at least one internal combustion engine and at least one electromotor, which together supply a drive torque, respectively a driving power output, for a motor vehicle. At a power output demand on the hybrid-electric power train, which corresponds at least to a lower power output threshold, the internal combustion engine is operated constantly at least approximately at the full load.