The term 'rapid heartbeat' is a medical condition known as tachycardia. Tachycardia is a condition in which the heart rate is abnormally fast, usually over 100 beats per minute. It can be caused by a variety of factors, including stress, anxiety, and certain medications. Symptoms of tachycardia include chest pain, shortness of breath, dizziness, and fatigue. Treatment for tachycardia may include lifestyle changes, medications, or surgery.