Ground plane can be improved quite a lot. With a better footprint placement I guess this PCB can be routed on a single layer. It is often also easier to route around two TL072 IC’s compared to a single TL074.
On a sidenote, you do not have to zip up all the zipped backups, and you can also delete the fp-info-cache from your zip files.
This reduces the archive size quite a lot:
2023-08-14_TL074_ECG_1010_V0.1.zip (235.7 KB)
Note, I also made some small routing improvements, but it’s nowhere near “ideal”. Learning to manually route a PCB is an art in itself and takes practice to learn. It also starts with making a better footprint placement.
I also guess that the diodes shown below are supposed to clamp the input signal to +/- a diode drop, if this is so, then turn one of them around.
I also have not seen any guard tracks yet on your PCB…
Also, for EEG / ECG it’s common to put transistors in the input protection, which are also supposed to limit fault currents through the electrodes in case something goes wrong.
You may want to have a look at OpenEEG:
The Board is apparently available in Eagle format, but KiCad can readily import this. There are also many other projects around. EEG is quite popular in the DIY market.