A method has been developed that detects cardiac arrhythmia from intrinsic cardiac nerve signals obtained from a heart in a patient. The method includes sampling intrinsic cardiac nerve activity at a high sample rate, filtering the sampled signal with a high pass filter, comparing the filtered signal to a predetermined threshold, and initiating a therapeutic action in response to the filtered signal exceeding the predetermined threshold. The intrinsic cardiac nerve activity may be received through an electrode implanted on the heart or from an electrode inserted into the venous structure of the heart.
