An implantable cardiac rhythm management (CRM) device includes a sensing and detection circuit that senses at least one cardiac signal and detects cardiac electrical events from the sensed cardiac signal using a detection threshold that is adjusted based on a dynamic noise estimation. The sensed cardiac signal is filtered to produce a filtered cardiac signal having a signal frequency band and a noise signal having a noise frequency band. The noise frequency band is substantially different from the signal frequency band. A dynamic noise floor is produced based on the noise signal and used as the minimum value for the detection threshold. A cardiac electrical is detected when the amplitude of the filtered cardiac signal exceeds the detection threshold.