Atrial fibrillation carries a risk of stroke. The heart, when it is in atrial fibrillation, the top chambers, or the atrium, are more or less just quivering, and blood flow through the top chambers does not move as efficiently as it would in a normal rhythm or in sinus rhythm. In this scenario, blood tends to pool in the corners of the heart and when that happens, clots can form. Those clots, if they dislodge from the heart, can land in other areas of the body. In a sense, approximately 50 percent of the blood flow goes to the head, so a stroke is probably the most common scenario that these blood clots can cause. The risk of a stroke can range anywhere from two to three percent in some individuals. And those with higher risk factors for stroke can be upwards of ten to 15 percent per year.