Abstract: An implantable cardiac device includes electrodes for sensing and pacing the heart, and optionally, defibrillation electrodes. The IECG with a noise component sensed in the heart is processed to derive raw sense signals indicative of whether the sensed QRS complexe's range is outside a certain range. This range is dynamically adjusted to compensate for the noise component. Preferably this range is defined by a threshold signal generator which generates a threshold signal including a first part which varies dynamically in accordance with a preset criteria and a second part which is at least equal to the peak amplitude of the noise.