Sometimes atrial fibrillation (AF) can lead to the following complications:
In AF, the chaotic rhythm may cause blood to pool in your heart's upper chambers (atria) and form clots. If a blood clot forms, it could dislodge from your heart and travel to your brain. There it might block blood flow, causing a stroke.
The risk of a stroke in AF depends on your age (you have a higher risk as you age) and on whether you have high blood pressure, diabetes, a history of heart failure or previous stroke, and other factors. Certain medications, such as blood thinners, can greatly lower your risk of a stroke or the damage to other organs caused by blood clots.
AF, especially if not controlled, may weaken the heart and lead to heart failure — a condition in which your heart can't circulate enough blood to meet your body's needs.
Source: Mayo Clinic