I am building an ECG sensor based on the AD620 instrumentation amplifier. The circuit is amplifying minute(50uV) signals from the signal generator perfectly. The total gain of the circuit is around 144. I get a problem when I try to extract the real ecg signal from the body. When the right arm and the left arm are connected, the output saturates which I think is because the inputs will be floating. The moment I connect the right leg drive to the right leg, the signal disappears and I get a very small signal (4mV) peak to peak at 50Hz. I think the problem is with the right leg drive,how can i solve this problem. I have attached the image of the circuit.