Having atrial fibrillation, an irregular heart rhythm, increases your risk of having a stroke. This irregular beating of the heart affects blood flow in the top chambers of the heart and can cause blood cells to collect and stick together, which increases the risk of a blood clot forming. These blood clots may then be carried in the bloodstream to the brain and, if large enough, can block an artery in the brain, resulting in a stroke. Oral anticoagulant drugs (commonly called blood thinners) are used to help prevent strokes by causing the blood to take longer to clot. Two groups of oral anticoagulant drugs are used, vitamin K antagonists (warfarin/Coumadin) and non–vitamin K antagonist oral anticoagulants (NOACs). This Cardiology Patient Page focuses on NOACs.