SOME 300,000 Brits are living with a stealth disease that could kill them within five years, doctors have warned. A third of those are likely to have no idea they are affected because they do not show clear symptoms. Aortic valve stenosis, or AS, is a heart condition that often shows no symptoms until it’s already too late. The condition is when the heart's aortic valve narrows, reducing or blocking blood flow from the heart into the main artery to the body (aorta). This can cause chest pain, dizziness, fatigue, or a rapid, fluttering heartbeat in the more severe and...