All pets that heal other pets use the heal as and when THEY decide to. You have no say in the matter, other than by putting them in passive, in which case they won't heal at all (unless that behaviour was changed in I7, can't say my PB's are ever in passive, so I haven't noticed)
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If 1 of your pets gets on low health, he runs over, finish his attack and does his heal. Interupted he wont try against straight after, but he does a attack first again.
Though it seems when all pets and you get damaged, he picks his MM prior to the fellow pets to heal.
And iirc, at lvl18 you get the 3rd pet, so that would be your lvl for the medic.
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
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Ah. Thanks guys. The populace will quake at the name of Red Square! 
In short, you get it at lvl 18 as your 3rd soldier.
Hello,
)
My Merc Mastermind, Red Square (chose Mercs purely froma theme point) is nearing level 12 and I was wondering if this was the level you recieve the medic? (I'm at work and can't get the time to read the guide before someone comes in the room
And does he heal automatically or is it a command?
Thanks in advance (sorry if youve answered this a thousand times)