On 6511-type ECG in a different frequency on the pulse for the analog signal, according to OFF, EMG, HUM and EMG + HUM, four mapping filtering state, the amplitude-frequency lines were drawn. When the lines show the OFF state, voltage does not attenuate and when using EMG, HUM, EMG + HUM state, voltage decreases with the increasing of pulse frequency. Based on the design principles of 6511-type ECG in filtering function the amplitude- frequency lines were ill ustrated theoretically, and heart disease, especially cardiomyopathies changes were determined, filtering will obviously result in ECG signals’ attenuation and distortion, resulting in missed diagnosis. Therefore, clinical ECG workers are proposed as far as possible not to use filtering, but to use of a number of practical interventions to reduce or eliminate outside interference on the impact of ECG.