Looking good! I couldn't resist, I just had to solder some of the components on it :)The bottom ground layer is without any major traces, set aside for the pads and traces for the memory card reader and the BT module where I removed all unnecessary pads, in order to improve the EMC.
With the 3rd revision still using a discrete components in the analogue front end, the question might beg of why I didn't go for a packaged ECG front end IC. Well, I still wanted this project to be mostly educational, and I believe working with discrete, analogue components like opamps and inamps promotes a broader knowledge in circuit design. I added test points to the PCB now, so that tracking the signal, testing and verifying becomes much easier.