Atrial fibrillation (AFib) causes high risk of stroke . It leads to a 5-fold higher risk of stroke and is responsible for 20% of all strokes[6-8]. Approximately 40% of AFib patients have no symptoms  so that many of them are diagnosed by coincidence when hospitalized for other reasons , including stroke [4, 5]
In the case of Atrial Fibrillation, the heart chambers beat chaotically and irregularly. This can cause blood to accumulate in the atria of the heart, clump together, and form blood clots. These blood clots can then migrate through the bloodstream to the brain, where they block the blood vessels and this causes a stroke.
The dangerous part of AFib is, that about 70% of the AFib episodes are asymptomatic and remain undiagnosed. In addition, at the beginning AFib generally appears only irregularly and can therefore be overlooked even during sporadic doctor's visits.
Some people with atrial fibrillation have no symptoms. And those who do have atrial fibrillation symptoms may experience signs and symptoms such as: 
The cause of Atrial Fibrillation is not fully understood. However, the following risk factors can additionally increase the risk of having AFib:
AFib is the most common sustained cardiac arrhythmia occurring in 5% of the population of 65 years and older and in 14% older than 85 years. AFib leads to a 5-fold higher risk of stroke and is responsible for 20% of all strokes. Many people have no symptoms from AFib and therefore remain undiagnosed. Early detection of AFib followed by adequate treatment can reduce the risk of a stroke by 68%. [7-9]