Amongst some definitions of the web search one can define, Atrial fibrillation is an irregular and often rapid heart rate that commonly causes poor blood flow to the body. Stroke on the other hand is, a medical emergency. Strokes happen when blood flow to your brain stops. Within minutes, brain cells begin to die. There are two kinds of stroke. The more common kind, called ischemic stroke, is caused by a blood clot that blocks or plugs a blood vessel in the brain. The other kind, called hemorrhagic stroke, is caused by a blood vessel that breaks and bleeds into the brain.