Stroke: the chaotic rhythm can cause blood to stagnate in the atria, forming clots. If a clot forms, it can detach from your heart and get into your brain. Once there, it could block the flow of blood, causing a stroke. The risk of stroke associated with atrial fibrillation depends on your age (the risk increases with age), hypertension, diabetes, previous history of heart failure, previous history of stroke, as well as other factors.
Anticoagulants may considerably reduce the risk of stroke or damage to organs caused by blood clots. Heart failure.
Arrhythmia, particularly if uncontrolled, can weaken the heart and cause dysfunction of the pump function. Your heart can then no longer circulate enough blood to meet the needs of your body.