1. A system for estimating an actual ECG signal of a patient while performing chest compressions with an automatic chest compressions device, said system comprising: an ECG sensor capable of measuring an ECG signal of the patient, said ECG sensor producing a measured ECG signal having an actual ECG component and a noise component; an automatic chest compression device adapted to repeatedly compress the chest of the patient disposed to provide chest compressions to the patient, said chest compression device having a load sensor capable of determining the presence of a chest compression when the load sensed by the load sensor exceeds a predetermined value, said load sensor producing a compression signal corresponding the presence a chest compression; a signal processing system operable to receive the measured ECG signal and the compression signal, said signal processing system programmed to estimate the noise component of the measured ECG signal with a system identifier by processing the measured ECG signal and the compression signal, combine the measured ECG signal and the estimated noise component of the measured ECG signal, and calculate the estimated actual ECG.