This paper presents low-power systematic integration of the instrumentation amplifier and the low-pass filter for portable ECG monitoring systems. To reduce overall power consumption, the electrode offset cancellation was carried out by sharing one operational transconductance amplifier (OTA) between the amplifier and the filter. Dual loops were implemented to provide offset cancellation so that the cancellation rage is extended. The analog front-end circuit is designed and simulated in a TSMC 90nm CMOS process. The total power consumption is 3.8 W from a 1-V supply voltage. Simulation results show that the achieved CMRR is 100.3 dB.