A method and implantable medical device for determining noise in response to a cardiac signal that includes sensing the cardiac signal, determining a sensing window in response to the sensed cardiac signal, the sensing window comprising a first portion and a second portion, determining a first derivative signal in response to the sensed cardiac signal within only one of the first portion and the second portion of the sensing window, determining a second derivative signal in response to the sensed cardiac signal within the one of the first portion and the second portion of the sensing window, determining whether an amplitude of the second derivative signal satisfies an amplitude threshold, and determining noise in response to the amplitude of the second derivative signal satisfying the amplitude threshold.