A heart rate of more than 100 beats after exercise is normal, but if the heart rate exceeds 100 beats due to other pathological factors, it may be dangerous. Normal human heart rate is 60~100 beats/min, heart rate more than 100 beats/min is called tachycardia, heart rate up to 120 beats/min or higher, may lead to the reduction of cardiac output, organ blood supply is insufficient, dizziness, low blood pressure symptoms, serious cases can be life-threatening. A low heart rate of less than 60 beats/minute may also lead to insufficient blood supply to the brain, dizziness and even fainting. The heart rate increases after strenuous exercise and can be restored after rest. Common causes of tachycardia include hyperthyroidism and heart disease. Common symptoms include palpitations (rapid heartbeat, often accompanied by panic), chest tightness, dyspnea and so on. Tachycardia should be examined in a timely manner in the hospital to identify the cause and treat it actively.