Parents want their children to have a steady, regular heartbeat. If the heart is not beating in the rhythm it should, there may be an arrhythmia. So, what is a normal heartbeat for a baby? The number of heartbeats is different for different age groups: newborn baby (from the time of delivery when the umbilical cord is tied until 28 days) heart rate: 90~180 beats/min; less than 1 year old heart rate: 80~160 beats/min; 1~3 years old heart rate: 80~120 beats/min; 4~6 years old heart rate: 80~115 beats/min; 7~12 years old heart rate: 70~110 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 changes in 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 irregular; observe whether the child often feels weak; what is the fastest heart rate of the child per minute and when; what is the slowest heart rate and what is the slowest heart rate per minute in order to help the doctor make a distinction between physiological arrhythmias or non-physiological arrhythmias. For non-physiological arrhythmias, further tests such as blood tests for electrolytes and cardiac enzymes, electrocardiogram, cardiac ultrasound, ambulatory electrocardiogram, esophageal electrocardiogram and endocrine and immune-related laboratory tests should be performed.