There are many kinds of strong interference in the ECG measuring. Their frequency bandwidths often overlap with that of ECG. It has been a big problem to remove these interference while keep as much useful ECG as possible for many years. The mathematical morphology is discussed in this paper and it's application in ECG is also presented. Compared with the normal linear filters, this non-linear filter has excellent capability in the removal of some kinds of common but important interference. Furthermore, mu...