When a patient develops atrial fibrillation, the electrical impulses that control the heartbeat are no longer ordered. Instead, many impulses begin to travel in different directions at the same time through the atria. Fast and chaotic impulses do not give the atria time to effectively contract and squeeze blood into the ventricles. Since the left atrial appendage is a small sac, blood easily collects in it, and the blood flow rate decreases, which contributes to the formation of clots – thrombi. When blood clots enter the left atrium and further into the left ventricle and aorta, they can cause stroke, myocardial infarction, and other ischemic events. People with atrial fibrillation are 5 to 7 times more likely to have a stroke than people with a normal heart rate.