Tachycardia is a heart rate that is too fast. Tachycardia occurs normally in times of stress, anxiety, or fear, but the heart rate returns to normal when the precipitating event or stimulus is removed. It also occurs as a normal response to intense exercise. In some medical conditions, the heart rate may be persistently elevated. Examples include certain arrhythmias of the heart. Thyroid diseases can also cause an elevation of the heart rate. The heart rate may be elevated when body temperature is high or due to taking certain medications. Cigarette smoking and excessive caffeine intake also cause tachycardia, as well as abuse of alcohol and recreational drugs. Other causes of fast heart rate include anemia, panic disorder, and diseases that damage the heart itself.