A baby’s fast heartbeat may be caused by physiological phenomenon, emotional influence, or disease. 1. Physiological phenomenon: The heartbeat of infants is faster than that of adults, which is a normal physiological phenomenon and generally does not require special treatment. With the increase of age, the heart rate will gradually approach the adult level. 2. Emotional influence: when the baby is particularly excited or sad, the heartbeat will be particularly fast, and after a period of time, the heart rate will gradually return to normal after the emotion is stabilized. 3. Disease: congenital heart disease, myocardial damage, pneumonia and other diseases may lead to a rapid heart rate, usually accompanied by dyspnea, wheezing and other abnormal symptoms. The baby’s heartbeat is particularly fast, may be due to disease. It is recommended that you take your baby to a regular hospital as soon as possible and follow the doctor’s instructions for treatment.