An automated external defibrillator for use during cardiopulmonary resuscitation comprising: an input of an ECG signal; a user interface having at least one of an aural instruction output and a visual display; an ECG analyzer in communication with the input and operable to determine a shockable cardiac rhythm in the presence of CPR-related signal noise artifact from the input; a memory for storing instructions related to a CPR rescue protocol that includes a period for providing CPR compressions; and a processor in communication with the ECG analyzer and the user interface, the processor operable to issue instructions via the user interface responsive to the determined shockable cardiac rhythm, wherein the ECG analyzer is operable to determine the shockable cardiac rhythm in the presence of CPR-related signal noise artifact from the input with a sensitivity of greater than about 70% and a specificity of greater than about 95%, wherein the input comprises a stream of digitized ECG signal data, and further wherein the ECG analyzer segments the ECG signal data corresponding to a predetermined time segment, wherein the ECG analyzer further comprises a set of fixed-frequency band pass filters which operate to filter the CPR-related signal noise artifact from the ECG signal data, characterized in that the ECG analyzer further comprises an algorithm which determines the shockable cardiac rhythm from both a measure of a filtered ECG signal data centered on one frequency at about 25 Hz and of a second filtered ECG signal data centered on a second frequency of about 35 Hz, and wherein the ECG analyzer further determines that the cardiac rhythm is shockable if both the filtered ECG signal data and the second filtered ECG signal data are below respective predetermined thresholds. an input of an ECG signal; a user interface having at least one of an aural instruction output and a visual display; an ECG analyzer in communication with the input and operable to determine a shockable cardiac rhythm in the presence of CPR-related signal noise artifact from the input; a memory for storing instructions related to a CPR rescue protocol that includes a period for providing CPR compressions; and a processor in communication with the ECG analyzer and the user interface, the processor operable to issue instructions via the user interface responsive to the determined shockable cardiac rhythm, wherein the ECG analyzer is operable to determine the shockable cardiac rhythm in the presence of CPR-related signal noise artifact from the input with a sensitivity of greater than about 70% and a specificity of greater than about 95%, wherein the input comprises a stream of digitized ECG signal data, and further wherein the ECG analyzer segments the ECG signal data corresponding to a predetermined time segment, wherein the ECG analyzer further comprises a set of fixed-frequency band pass filters which operate to filter the CPR-related signal noise artifact from the ECG signal data, characterized in that the ECG analyzer further comprises an algorithm which determines the shockable cardiac rhythm from both a measure of a filtered ECG signal data centered on one frequency at about 25 Hz and of a second filtered ECG signal data centered on a second frequency of about 35 Hz, and wherein the ECG analyzer further determines that the cardiac rhythm is shockable if both the filtered ECG signal data and the second filtered ECG signal data are below respective predetermined thresholds.