Uniquely, AF is an eminently preventable cause of stroke with a simple and highly effective treatment. AF is common and affects over 600,000 patients in England (1.2%). It is a major predisposing factor for stroke, and strokes caused by AF can be particularly severe and disabling. The annual risk of stroke is five to six times greater in AF patients, but treatment with warfarin can reduce the risk of stroke by 50-70%, and the safety and efficacy of warfarin in older people has been clearly demonstrated.