A stroke happens when the flow of blood is cut off to part of your brain. Most are caused by a clot or something else that blocks the flow. These are called ischemic strokes. About 10% are caused by bleeding in the brain. These are hemorrhagic strokes.Older age and family history of strokes are among the things that make you more likely to have a stroke. You can’t turn back the clock or change your relatives. Still, experts say 80% of strokes can be prevented. A quarter of Americans who have strokes have had one before. So what can you do to tilt the odds in your favor?