Second degree AV block is a condition in which there is a partial interruption of conduction from the atria to the ventricles, i.e., there is a ventricular leak, which may be accompanied by delayed AV conduction. The common subtypes of second degree AV block are second degree type I and second degree type II. According to the different types, its etiology is also different, as follows: 1. Second degree type I AV block: often occurs in acute reversible or self-limiting diseases, such as acute infarction, acute myocarditis, overdose of anti-arrhythmic drugs, such as digitalis, amiodarone, beta-blockers, etc.; also seen in vagal tone is too high, the atrial rate is too fast; 2. Second degree type II AV block: clinical Commonly seen in coronary artery disease such as acute anterior interval myocardial infarction, cardiomyopathy, idiopathic double bundle branch fibrosis, myocarditis, hypertensive heart disease, toxic reactions to antiarrhythmic drugs such as digitalis, quinidine, β-blockers, etc. Other infections: such as coxsackie B virus infection, measles, mumps, viral upper respiratory tract infection, infectious mononucleosis, viral hepatitis, typhoid fever, etc. can cause extensive or localized damage to the conduction system, etc.