A heart block is a disruption in the conduction of an excitatory impulse from the heart along the conduction tissues, where the impulse can partially or completely fail to pass. The mechanism of occurrence is an abnormal prolongation of the myocardial electrophysiologic stress period, and the block can be temporary, intermittent, or permanent. Transient or intermittent block can be caused indirectly by increased vagal tone or directly by disease or drug action on the myocardium; permanent block is the result of organic cardiac disease, except in rare cases due to congenital abnormalities. Conduction block can occur in any part of the heart, and according to the location of conduction disorders, heart block can be divided into four categories: sinus atrial block, atrial block, atrioventricular block and intraventricular block. Among them, atrioventricular block is the most common in pediatric patients, followed by intraventricular block. The causes of conduction block include acute infections such as rheumatic heart disease, viral myocarditis, cardiomyopathy, myocardial ischemia, congenital heart disease (such as atrial septal defect, tricuspid valve subluxation malformation, transposition of large vessels, etc.), drug and electrolyte disorders (such as digitalis, quinidine, antiarrhythmic drugs such as cardioplegia, isoptin, and hypokalemia, etc.), and cardiac surgical injury, etc. Sinus block refers to conduction block occurring in the continuous sinus tissue. Sinus node impulses in the process of conduction of the atria, according to the degree of conduction disorder, in theory, sinus block can be divided into three degrees, namely, degree I, degree II, and degree III. Sinus conduction block is often temporary, but there are also long-term persistent or recurrent effects. It is seen in healthy individuals with vagal hypertonia or sinus hypersensitivity, and also in children with various acute myocarditis, in addition to digitalis, quinidine, β-blockers or hyperkalemia, which can also cause sinus conduction block. Transient sinus block is often asymptomatic, while prolonged sinus block may produce dizziness or even syncope. Persistent third-degree sinus block without escape rhythm causes cardiac arrest, which can be fatal. Sinus atrioventricular block is one of the causes of Athlete’s syndrome. Atrioventricular conduction block, which occurs in the atrioventricular junctional tissue, is an abnormal delay or interruption of atrioventricular conduction due to prolonged atrioventricular junctional tissue overload. First degree AV block can be seen in healthy individuals, but it is more common in patients with heart disease. Rheumatic myocarditis, acute viral myocarditis, and digitalis toxicity are common causes of first degree AV block. Atrioventricular block of degree I has no significant effect on hemodynamics and does not cause symptoms. The diagnosis is confirmed by a prolonged P-R interval on the electrocardiogram. The symptoms of Ⅱ° AV block are related to the fast or slow ventricular rate, such as occasional ventricular leakage, which is often asymptomatic, and more leakage, palpitations, chest tightness and weakness, dizziness and other symptoms when the ventricular rate is slow, and most cardiac auscultation has arrhythmia, which can be irregular or regular leakage, and the first heart sound can be of varying intensity, but sometimes it can be a slow and uniform rhythm. III° AV block has palpitations, dizziness, weakness, chest tightness, and limitation of motion because the heart rhythm is very slow. In severe cases, syncope, an attack of A-Syndrome, may occur. Systolic and early-mid diastolic murmurs are often heard at the left sternal border and apical region when the heart rate is slow, and a third heart sound, or even a fourth heart sound, with variable intensity of the first heart sound and sometimes a large cannon sound, may be heard. The pulse pressure difference is large. Electrocardiogram can be done to confirm the diagnosis in those who have the above symptoms. For the treatment of conduction block, the first step is to actively treat the primary disease and eliminate the cause of conduction block. Secondly, medication is used. The first degree of conduction block does not require special treatment. For those who have a slower heart rate and conscious symptoms of maladjustment in the second degree or higher conduction block, atropine and isoprenaline are available. Acute occurrence of degree III AV block should be treated with hormone therapy. Sometimes an artificial pacemaker is needed for third-degree AV block.