Atrial fibrillation (AF) is a heart condition characterized by rapid, irregular beating of the left atrium or upper chamber of the heart. These abnormal contractions are weaker than normal ones, resulting in sluggish blood flow within the atrium. When blood pools and becomes stagnant, it can lead to the formation of blood clots. If a clot dislodges from the heart and travels to the brain, it can block blood flow through brain arteries, causing a stroke.