Heath, 87, flown home to hospital.
The ex-MP was flown by air ambulance from Salzburg yesterday morning after suffering a suspected pulmonary embolism - a blood clot on the lung.
Sir Edward was flown to London's RAF Northolt airbase after being picked up from Salzburg's main hospital, Landeskrankenhaus.
It was believed Sir Edward, 87, was taken to the King Edward VII hospital in central London.
A hospital spokeswoman said they had been told to refer any calls regarding Sir Edward to his private secretary.
King Edward VII Hospital was originally opened to care for sick and wounded officers returning from the Boer War. It is a private independent acute hospital which still cares for serving and retired officer patients as well as others.
Although the seriousness of his condition is unknown, it is understood Sir Edward was well enough to give instructions to his staff.
Pulmonary embolism is a condition commonly associated with so-called 'economy class syndrome' or deep vein thrombosis.
The sometimes deadly clots, usually originating in the veins of the leg in the form of DVT, can break free and travel up the body. There they can become lodged in one of the vessels which supplies the lungs.
Rumours about the health of Sir Edward have been circulating in Westminster for several weeks.
Sir Edward left the Commons at the June 2001 election after serving as MP for Bexley and Old Sidcup for 51 years.
A non-smoker who rarely drank, he fought the 1997 general election and has remained in good health throughout his life.