The most common symptoms are irregular heartbeat, fast heart beat, dizziness and lightheadedness, heart palpitations that feel like a sudden pounding or racing in the chest, fatigue, or shortness of breath. Some people may have chest pain. When atrial fibrillation affects the pumping of your heart, your blood pressure may fall and you may feel lightheaded or faint.  Occasionally, the first symptom is a stroke, caused by a blood clot that formed in the fibrillating atrium and traveled to the brain.  Some people have no symptoms.