Heart rate of 120 means heart rate of 120 beats/minute, and the normal heart rate of adults is usually 60~100 beats/minute. If it is a fetus or an infant, it is usually a normal heart rate, and if it is an adult, it belongs to tachycardia. 1. Fetus, infants: Fetus, infants are in the stage of rapid growth and development, due to the development of the body needs to consume a lot of oxygen and nutrients, so the heartbeat is relatively fast, in order to maintain the supply of oxygen and nutrients needed by the body, so the heart rate is faster, the fetal heart rate of 110 ~ 160 beats / min, infants 110 ~ 130 beats / min, heartbeat of 120 at this stage is a normal heart rate. 2. Adults: With the gradual improvement of physical development, the metabolism decreases, and the heart rate also decreases gradually. The normal heart rate of adults is usually 60~100 beats/min, if the heartbeat is 120 beats/min, then it is tachycardia, which may be caused by physiological reasons, or it may be caused by diseases. (1) Physiological reasons: such as citing coffee, emotional excitement, etc., will lead to a transient increase in heart rate to 120 beats / min, coffee metabolism is completed or emotional calm, the heart rate will return to normal. (2) Disease: mostly seen in arrhythmia, hyperthyroidism, myocarditis, etc., due to a variety of reasons lead to sinus node excitation, myocardial contraction accelerated, etc., the occurrence of heartbeat 120 times / min, need to do under the guidance of the doctor to target the treatment, such as arrhythmia can be used in accordance with the doctor’s instructions, such as metoprolol. All of the above drugs need to be used under the guidance of a doctor, if you need to clarify the condition, it is recommended to go to the hospital to do a detailed examination.