A defibrillator – which delivers an electric shock to restart a person's heart if they have a cardiac arrest – has been installed at The View from The Shard visitor attraction.
"When you have a cardiac arrest, your heart stops beating and you are clinically dead," said London Ambulance Service chairman Richard Hunt CBE.
"Every second counts which is why we want more public-access defibrillators to help us save more lives in London."
The new defibrillator is part of London Ambulance Service's Shockingly Easy campaign to get at least 1,000 extra defibrillators in shops, businesses, gyms and high footfall areas across London.
Around 28 per cent of people survive an out of hospital cardiac arrest but, where there is a defibrillator and someone trained to use it, the chance of survival can increase to 80 per cent.
When someone goes into cardiac arrest, it is the first three or four minutes that are crucial – that is when they need to receive cardiopulmonary resuscitation (CPR – chest compressions and rescue breaths) and defibrillation.
Sandy Clark, operations director of The View from The Shard, said: "We are proud to be the home of Europe's highest defibrillator.
"The View from The Shard welcomed one million guests within our first year, and we know that having this equipment and properly trained staff to use it could help us save a life in the future.
"We urge every business in London to get a defibrillator installed. If we can install one at one of the highest points in Europe, then anyone can do it!"