This paper describes the designing of a fourth order low-pass filter (LPF) for portable ECG application. The proposed filter is designed by cascading one P-biquad and one N-biquad to form a fourth order filter. It is self-compensated and provides a 0 dB gain. It also acquires the same input and output common mode voltages, which helps to produce higher order filters. It consumes power of 7.2 nW with a supply voltage of 1.2 V. Dynamic range of 68.1 dB with noise of 61.2 µVrms is obtained. The proposed filter is designed for a cut-off frequency of 230 Hz, suitable for ECG application. With 100 Hz frequency and 100 mV_pp ac amplitude, HD₃ of 71 dB is achieved. The circuit is simulated in cadence software using Silterra 130 nm CMOS technology. Compared with other state-of-the-art designs, this novel LPF provides the largest dynamic range and the best figure of merit (FOM).