The causes of tachycardia are as follows: 1. Functional factors: such as emotional anxiety, mental stress, pregnancy status, work reasons, etc.; 2. Organic heart disease; 3. Extracardiac factors: such as fever, anemia, hyperthyroidism, severe infections, etc., which are related to the increase of sympathetic excitability and the decrease of vagus nerve excitability; the younger the age, the quicker the heart rate is, so that children’s heart rate tends to be quicker. Once tachycardia occurs, electrocardiography should be actively performed to clarify the cause and treat the symptoms.