It is very effective at significantly reducing the risk of stroke in people with atrial fibrillation (AF), an irregular abnormal heart rhythm. About 60 per cent of people taking warfarin have AF. The condition can lead to pooling of blood in the heart chambers, which increases the risk of clots forming. If these clots are ejected by the heart, they can lead to a stroke. Warfarin helps to prevent the clots from forming.
People who are prone to blood clots in the circulation outside the heart are also often prescribed warfarin: for example, people who have had deep vein thrombosis (DVT) and those who have had clots travel to the lungs, causing a pulmonary embolism. People who have had a mechanical heart valve replacement are often prescribed warfarin to prevent clots forming on the valve. Warfarin can also help stop the mechanical valve from failing; if the valve becomes encased in blood clots, it can stop working properly.