The most serious complication of atrial fibrillation is a stroke caused by a blood clot in the brain. During atrial fibrillation, blood clots can form in the heart. Clots may then travel in the bloodstream to the brain, where they can block blood flow to a part of the brain and cause a stroke. The risk of a stroke can be reduced by blood thinners.  Take your medicines as prescribed. If you take blood thinners, keep appointments for follow-up blood tests.  Contact your doctor right away if you have any new symptoms or symptoms that come back, such as falling or fainting.  The best prevention is to have a heart-healthy lifestyle. Eat a healthy diet, stay fit with the right kind of exercise for you, do not smoke, and limit your use of alcohol. If you have heart disease or high blood pressure, follow your doctor's advice closely.