more information about my issue :
I used both method to see what's happening.. Digital/Analog Read functions (D7/A0 port).
Yes.. I connected sensor on digital and on Analogic port..
I used 2 python scripts.
One reading values comming from D7 port and another one reading values comming from A0 port.
and in both modes, I can see data changing like a heartbeat :
in D7 mode, of cource, the 1 value seems to correspond to my heartboard
in A0 mode, same with 1023 or 1022 values but more accurate
in my scripts, I do not use time.sleep function in the loop.