Atrial fibrillation (AF) is a rapid heart beat increasing the risk of blood clots and stroke.

Atrial fibrillation is the most common abnormal heart rhythm. The risk of having AF increases with age, with about 8% of people aged over 80 having this condition.

Atrial fibrillation is often asymptomatic (with no noticeable symptoms), and isn't usually life-threatening. People may notice heart palpitations, fainting, or chest pain as a result of AF.

People with AF have an increased risk of stroke compared to people whose heart is beating in a normal rhythm. The risk of stroke increases in AF because blood may pool and form clots in the heart. It is when these clots break off and travel to the brain that a stroke may occur.

Warfarin reduces the risk of stroke in AF by making it harder for your blood to form clots in the heart.