The regular beating of the heart is one of the first life phenomena to come to human attention. It is no exaggeration to say that once your heart stops beating, your life stops. By the same token, if your heart is beating slowly, your life is at stake. Because children are still developing and have a faster metabolism, their heart rhythm is generally faster than that of an adult. For adults, a heart rate of 60 beats or more is acceptable, but for children 60 or so is far from enough. A newborn’s heart rhythm is generally required to be 120-140 beats per minute, 100-120 beats per minute at 2-3 years of age, 80-100 beats per minute at 4-7 years of age, and slowly similar to that of an adult only after the age of eight. Children have smaller hearts, which means that more beats per minute are needed to maintain a normal cardiac output to supply the body’s needs. Therefore, once a child’s heart rate becomes slow, the heart has to activate its own regulatory mechanism by passively enlarging the heart, thereby increasing its volume so that more blood can be pumped out with each beat, thus meeting the body’s needs as much as possible with a limited heart rate. However, the enlargement of the heart is not infinite, and at a certain point, the heart cannot be enlarged, and at this point, the heart will fail due to the excessive elongation of the heart fibers, just like a rubber band being broken after being excessively tightened, resulting in the clinical manifestation of severe cardiac insufficiency. There are two major causes of slow heart rate in children: one is congenital, which means that the child is born with a poorly developed heart conduction system, which causes the heart rate to go fast and slow, and then slowly get slower and slower. The other major category is acquired, which means that the conduction system was not a big problem, but during the repair of the congenital heart malformation, the conduction system and the heart defect were close together, which led to intraoperative damage to the conduction system, resulting in what is called high atrioventricular block. For the first major category, which is congenital slow heart rate, parents tend to detect it rather late. This is because the child usually has no specific symptoms and can grow up normally. It is only during a physical examination, or when the child shows signs of heart failure, that the heart is found to be very slow and enlarged. For these children, it is very difficult for parents to make up their mind to treat them, because they always feel that the child is not bad, and that he or she will get over it. However, this is a very bad idea, because if this continues, the child’s quality of life will be poor, because his/her heart rate is not stressful and cannot increase during exercise, so the child cannot play with healthy children, but can only stay quietly; on the other hand, the heart will continue to expand, and if serious heart failure occurs, the treatment will be very difficult, and even the installation of a pacemaker may not solve the problem. The other aspect is that the heart will continue to expand, and if severe heart failure occurs, the treatment will be very difficult, and even a pacemaker may not solve the problem. For the second major category, which is acquired slow heart rate due to surgical injury, there is no doubt that the heart cannot be palliated and pacemaker installation should be actively considered. It is not uncommon for heart rate changes to occur after cardiac surgery, but the vast majority return to normal within 2 weeks after surgery. Only those with severe conduction system damage during surgery require a pacemaker, which is about 5% of all cardiac surgeries. Therefore, if a child with a precordial disease does not return to a normal heart rate within two weeks of surgery, then a permanent pacemaker should be considered.