Prevention includes decreasing risk factors, surgery to open up the arteries to the brain in those with problematic carotid narrowing, and anticoagulant medication in people with atrial fibrillation. Aspirin or statins may be recommended by physicians for prevention. Stroke is a medical emergency. Ischemic strokes, if detected within three to four-and-a-half hours, may be treatable with medication that can break down the clot, while hemorrhagic strokes sometimes benefit from surgery. Treatment to attempt recovery of lost function is called stroke rehabilitation, and ideally takes place in a stroke unit; however, these are not available in much of the world.