Approximately 2.7 million people in the United States have atrial fibrillation. It is the most common type of heart arrhythmia (irregular heartbeat) that can interrupt the normal flow of blood. This interruption means the condition puts you at risk for blood clots and stroke. Atrial fibrillation may be temporary, may come and go, or may be permanent. However, with regular medical care, you can live a normal, active life.