" ...not intended, authorized, or warranted for use as components in applications intended to support or sustain life."
If you don't plan to sell it as a medical product, measuring pulse frequency, temperature, blood pressure or other vital signals is a nice application to test sensors. (a lie detector is not supposed to sustain life ?)
I would not really fear to connect some high impedance sensor input wires to my skin.
But if google does not reveal such use cases, I'm not sure you find much help for your very generic question.
Arduino is fast enough to measure a few analog channels with signals in the 0-1V range with the required speed ( ~10Hz ).
You probably need some opamps to get signals in the proper range.
Hardware questions how to get usable signals is the more challenging part...
And the "...graph" ( output ) part is another question. I guess you want to transfer data to a PC and display your "cardiograph" there.