The aims of this study are enhancement the performance of low pass FIR
(Finite Impulse Response) Filters by using adjustable window design method, and reduce the amplitude of side lobes and Gibbs phenomenon problems in these filters,also study the effect of different orders of low pass FIR filters (20th ,70th, 200th ) on its performance when the parameter β in fixed value in the time domain and frequency domain, and investigate the effect of different values of parameter β=0.5,3,6,9 on its performance when the filter order in fixed value in the time
domain and frequency domain.These filters are used in the ECG signal applications to remove high frequency noise. The simulation of design these filters is implementing by using FDA tool (filter design and analysis tool) and wintool (window tool) from matlab (R2010a)
program. The study results have been obtained the lowest value of relative side lobe attenuation= -66.2dB with thin main lobe width = 0.016602 when the filter order and the parameter β are equal to 200th, 9 respectively, we find that Kaiser window function is the optimum window to reduce side lobe amplitude and to reduce the Gibbs phenomenon with control of the main lobe width as compared with other windows such as Hamming, Bartlett, Blackman and Rectangular, and gives much better stop band attenuation than the Parks-McClellan algorithm.