FIR filter is one of the best choices for ECG signal processing because of its linear phase property. With frequency response masking (FRM) technique, the multipliers needed to implement FIR filter can be reduced dramatically. This paper proposes an architecture for asymmetrical bandpass FIR filter based on the FRM technique. The optimum interpolation factor for the filter is derived and the design procedure for all the sub-filters is given. A design example is included to illustrate the effectiveness of the proposed filter for ECG signal processing. It shows that the filter can fulfill the design objectives with 70.3% less multipliers comparing to the conventional FIR synthesizing technique.