How input offset voltage (2mV max) will effect input which is at 0.5mV and 0.5 to 5Hz frequency? The input voltage and frequency are of heart vibrations which will be very low.
If your signal is 0 V to 0.5 mV, the input offset could be 4 times your signal (2 mV/0.5 mV). In practice, the problem is that if you want to have a high gain to amplify your signal (e.g. 500x), then the input offset will have a significant impact on the output, as it will be amplified as well and it will end up being a voltage range that you cannot use. If you are only interested in the AC component, you can have a band-pass filter to remove the offset, but the voltage range will still be limited by your op-amp output voltage range - (input offset*gain).
For very small signals like this, you should look into instrumentation or differential amplifiers with low input voltage offset and make a two-stage amplifier. For the second op-amp, the input signal will be larger enough, thus, you can choose one with more relaxed specifications.