The heart rate of infants is generally faster than that of adults, and it will slowly slow down with age. The heart rate of infants is affected by many factors, and parents should be alert to the phenomenon of arrhythmia in infants, so how much is the heart rate of babies normal? The number of heartbeats is different for babies of different ages: newborn (from the time of delivery when the umbilical cord is tied until 28 days) heart rate: 90 to 180 beats/min; less than 1 year old heart rate: 80 to 160 beats/min; 1 to 3 years old heart rate: 80 to 120 beats/min; 4 to 6 years old heart rate: 80 to 115 beats/min; 7 to 12 years old heart rate: 70 to 110 beats/min. The normal heartbeat originates from a starting point called sinus node, which starts the excitation needs to be broadcast according to a certain path, frequency, sequence and speed, making the heart to beat regularly, i.e. heart contraction and diastole activities. If any of the path, frequency, sequence and speed of the heart’s starting point and propagation process is abnormal, it will lead to arrhythmia. Common factors leading to tachycardia: mental stress, crying, breastfeeding, feeding, exercise, pain, fever, hypovolemia, anemia, heart failure, myocarditis, hyperthyroidism, and after the application of drugs such as epinephrine and atropine. The mechanism of its occurrence is mainly related to increased sympathetic excitability or decreased vagal tone. Common factors leading to a slow heartbeat: hypoxia, hypothermia, central nervous system damage, increased intracranial pressure, acidosis, obstructive jaundice, pituitary or hypothyroidism, and after the application of drugs such as digitalis and beta-blockers. Parents can try to feel the pulse when the child is uncomfortable whether it is fast or slow, flush or not; observe whether the child often feels weak; what is the fastest heart rate of the child per minute and when; when is the slowest heart rate and what is the slowest heart rate per minute. Generally speaking, if the child does not have chest tightness or breath-holding, the general condition is better and the problem should not be serious. Parents can go to the hospital for an electrocardiogram if they are really unsure.