Accumulate 7000 heal points in a single life.
Difficulty: Easy - Medium
How to: Play maps where a lot of people require healing constantly, such as Dustbowl or Goldrush or play at the back of a map but near teammates taking damage (the sniper deck on 2Fort is ideal, though be mindful of local server rules regarding this tactic). Stay out of the enemy line of fire and have some form of cover in sight at all times, and make sure to always keep moving and looking around so that Snipers and Spies can't get easy kills on you. One way to build up points is by backing up two Heavies by yourself and continually heal both as they get into the action; few people will target a Medic over two Heavies. Know when to cut your losses and ditch your Medic buddy if your situation is hopeless; even if you build up multiple ÜberCharges (which you should), be sure not to accompany your buddy on suicide runs unless you are 100% sure that you will survive. Playing on 27/7 CTF servers that have the time and capture limits disabled can make this achievement easier as you don't have to work against the clock. You can press TAB to see how much total healing you have done, though this will be the total amount of time while on that server, so subtract your total healing points at the beginning of the round. Keep in mind that overheal points still count as healing done; this means that during the round setup time, you should overheal every person on your team, this alone can net you 1000 heal points before the round has even started. Be sure to overheal everyone you see (within reason) when the round actually starts, Engineers, Snipers, and Spies often get overlooked when it comes to overhealing, but that's 75 healing you're passing up if you don't overheal them, and it only takes a second anyway. You will not receive progress on this achievement while you're earning it and you will not earn it until you die.
Find a map that will take a long time, such as a Territorial Control Map like Hydro, stay in your base + just overheal people as they respawn.
You just have to hope the game takes long enough for all your overheals to add up.