Atrial fibrillation, or a-fib, is an irregular and often very fast heart rate that can increase a person’s risk of stroke, heart failure, and other heart-related complications. It occurs when the two upper chambers of the heart (the atria) beat irregularly and not in coordination with the two lower chambers (the ventricles). This can lead to blood pooling and the formation of clots, which can get stuck in blood vessels and stop blood flow.

A stroke occurs when blood flow to the brain is blocked and the brain is unable to get oxygen and nutrients. A stroke is a medical emergency that must be addressed right away. Signs of a stroke include headaches, sudden weakness, trouble seeing, and numbness or paralysis of the face, arm, or leg—often only on one side of the body.