Every 40 seconds, someone experiences a stroke. It’s a startling statistic that impacts so many lives. But by knowing how to prevent stroke, identify symptoms and understand treatment, we can lessen the impact of stroke in the U.S. Strokes are caused by either a blockage of blood flow to the brain or a broken blood vessel leading to internal bleeding within the brain. Ninety percent of strokes are caused by blocked blood vessels causing the brain to no longer receive oxygen and nutrients.