Firstly Heathrow does have an Ambulance Staion, its in the Old Fire Station on the Northern Perri. At Some stage, by the nature of things all the ambulances there will be on calls elsewhere, its a fact of life. The BAA used to have an Ambulance manned by the Airport Fire Servide, it was a good service but just like the LAS it was unavailable at times. The LAS took it over in the 1980's and rest assured that things are better now then they were then, I spent 45 mins pumping on someones chest waiting for an ambulance in 1983.