A stroke that occurs when the flow of blood to a part of the brain is interrupted by a partial or complete thrombosis of the supplying artery or arteries, or by a clot of blood that has detached itself from elsewhere in the circulatory system for instance, a deep vein thrombosis (DVT) and blocked a cerebral artery. Stroke is the second most common cause of death worldwide. Its treatment is difficult and prevention is best targeted at those who are at the highest absolute risk of stroke, because such people are likely to derive the greatest benefit. They may have had a previous ischaemic stroke or transient ischaemic attacks or episodes (TIA, TIE), coronary heart disease or peripheral vascular disease. In the UK strokes affect about 200 people per 100,000 population annually, with the incidence rising sharply after the age of 55. At the age of 70 the incidence is around 15 people per 1,000 of population; at 80 the figure is double that.