If set to yes, this building heals any infantry units that enter it. The building must also have Ammo set to a value greater than 0 to specify the number of times it can heal infantry.
Note that giving the BuildingType a weapon will use up one Ammo each time the weapon fires and makes the building permanently unusuable (no firing, no healing) once it runs out of Ammo.
Note
While this flag is still valid in Yuri's Revenge, YR Hospitals use InfantryGainSelfHeal instead.
Adding some tags (which tags?) will make InfantryTypes unable to receive treatment.
Using this on a building that also has Factory=UnitType or Factory=InfantryType set causes the AI to spam only one type of unit from that factory, the first vehicle/infantry type that the AI can build (i.e. the AI house is listed as the object's Owner).