The most important operation of electrocardiogram (ECG) signal measurement device is to amplify signal and maintain correct original signal. The operation of all circuits cause electromagnetic interference (EMI), but EMI can be reduced by using special component or some PCB layout approaches. This paper provides an example of portable ECG device to demonstrate a method that can effectively reduce EMI and be applied in finished product. This research has built a lead-1 ECG to reach a low noise operation. This result can be easily applied to portable ECG measurement.