Check out this really compact electrocardiogram that someone made from a really tiny LCD, a pair of electrodes, and an ARM training unit. Its an STM32 Primer at the heart of the unit.
All you have to do is press your thumbs on the two electrodes and it will start the ECG trace. Then it will beep when it detects the pulse and will display the heart rate in decimal format in the upper left hand corner.
These things, if mass produced, and if proven accurate enough, could be very useful in the field, although they already have fairly portable, highly accurate ECGs for field personnel, so its allocated to just a fun toy. In case you got it in your head that making your own would be cool, those ARM development boards aren’t cheap, cheapest one I could find was on Ebay and cost $225, but it did come with a 3.5” LCD and the board.