Most manufacturers of instrumentation amplifier ICs have the design for an ECG amplifier in the datasheets. Then you simply copy the circuit without designing anything.
Look at the datasheet for an INA326 or an AD620A instrumentation amplifier IC for two of many example circuits.
u can use this circuit diagram.. i get nearly original ecg signal.
figure shows my ecg signal.
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(the last part of circuit is T twin 50hz noise filter)