The sinus node is the “headquarters” of the human heartbeat, and it has a large fluctuation range, from 40-60 beats per minute when it is slow (e.g., during sleep) to 180 beats per minute when it is fast (e.g., during strenuous exercise), which varies slightly with age and each person, but is basically in this range. However, although the sinus node is the headquarters, there is another important “transit point”, which is the “atrioventricular node”. The “heartbeat” sent by the sinus node, the command, must pass through the “atrioventricular node” before it can really be transmitted and the number of “heartbeats” can really be realized. Usually, this node is very strong and can relay all the heartbeats from the sinoatrial node. However, if the atrioventricular node is damaged, this relaying ability will be impaired. If the atrioventricular node is able to relay and transmit all the heartbeats from the sinoatrial node, but at a slower rate, this is called a “first degree block”. If the atrioventricular node is more impaired, then the transit and downward transmission will not go down (i.e., the phenomenon of cutting corners), and this is called “2nd degree AV block”, which is divided into type 1 and type 2, the latter being worse than the former. For example, the sinus node is 80 beats per minute, while the heartbeat is actually only 70. Of course, some cases of 2nd degree AV block, such as those that occur briefly during sleep, do not necessarily mean a serious problem, and if there are no symptoms, they can be closely observed and followed up in conjunction with the clinical situation. If the atrioventricular node is severely damaged and has completely lost its transit and downward transmission function, the heartbeat of the sinus node will not be transmitted downward, and the human body will be in danger of having a slow heartbeat. If the atrioventricular node is not able to transmit downward, but certain heart tissues below the atrioventricular node are capable of self-reliance and making their own decisions, a certain frequency of heartbeat can occur, but its ability is often poor, usually only about 40-60 times per minute, even if it is more vigorous activity, it is difficult to increase this frequency, the consequence is that when the activity (when the heartbeat needs to speed up), can not meet the body’s needs and there is weakness, weakness, etc. Weakness and other manifestations, however, in quiet time, due to the reduction of the actual human demand, there may not be a significant feeling. If the ability of “self-reliance” is very poor, only 30-40 times per minute, it is difficult to meet the needs of the body, there will be blackness or even fainting.