EMS Guide - What do I do?

Well... you revive players and heal them up. You can revive players by coming up to them when they are critically wounded and interacting with them. Please note that you cannot revive wanted players during an active shootout around them. While you are reviving, you are stuck in an animation and taking damage automatically makes the revive fail. You can heal players by going into some marked EMT vehicles and driving next to them. Press the on screen button to heal them and get a bit of cash.

Note - some medics have reportedly airlifted trucks full of cops onto skyscraper combat zones with dangerous criminals on top, try not to do that...