I have attached a schematic diagram of ECG device that i builded. it is based on ECG device given from AD620 instrumentation amplifier datasheet..i ve tested the first part of the circuit (AD620 and AD706 right leg driver)using oscilloscope but the signal i was getting it was not a proper one.when i attached the RA and LL electrodes i could see a signal looking like an ecg but not a proper one but when i was connecting the RL (ground) the signal disapeared.can anybody tell me why? now i have builded the whole circuit with a high pass filter after the AD620 of cut off frequency 0.025Hz and an operational ampliier of G=143.does the circuit looks ok or shall i make some changes? shall i include a resistor at the non inverting input of the last op-amp for input impedance?