In general, the disclosure is directed to a frequency selective monitor and methods for monitoring physiological signals in one or more selected frequency bands. A frequency selective monitor may utilize a heterodyning, chopper-stabilized amplifier architecture to convert a selected frequency band to a baseband for analysis. The frequency selective monitor may be useful in a variety of therapeutic and/or diagnostic applications. As examples, a frequency selective signal monitor may be provided within a medical device or within a sensor coupled to a medical device. The physiological signal may be analyzed in one or more selected frequency bands to trigger delivery of patient therapy and/or recording of diagnostic information.