Break FETTUCCINI in half and scatter inside the Instant Pot.
Pour WATER and HEAVY CREAM over the pasta. Push the pasta under the liquid to submerge it.
Scatter BUTTER pieces and GARLIC over the pasta noodles.
Lay CHICKEN BREAST on top of the pasta and sprinkle SALT and PEPPER over it. (Yep, we cook chicken breast whole and shred it later so it retains its juices)
Secure the lid; turn pressure valve to "Sealing" and pressure cook on HIGH for 5 minutes.
When cook cycle completes, let the pot sit undisturbed for a 10-minute (NPR) natural pressure release. DO NOT SKIP THIS STEP!
Safely turn pressure valve to "venting" position and release any remaining steam. Open the lid and transfer chicken to a plate.
Insert a meat thermometer in the center of the chicken breast to confirm a MINIMUM internal temperature of 165° then cover with foil and rest it a few minutes.
Stir the pasta and liquid together (it's not a pretty alfredo yet, but it will be).
Stir in PARMESAN CHEESE and adjust SALT and PEPPER, if needed.
Shred the chicken with two forks and stir it in to the pasta alfredo.