The clinical differentiation between physiological or pathological degree II AV block must be made by combining various clinical examinations with the etiology and clinical manifestations. 1. Physiological AV block: In most people with normal AV conduction function, rapid atrial pacing can induce ventrogenic AV block. In the case of graded incremental atrial pacing and paroxysmal atrial, atrial flutter, and junctional tachycardia, the atrial cycle is significantly shorter than the effective atrioventricular node induction period, resulting in partial supraventricular excitation that cannot be transmitted down to the ventricles and atrioventricular block. This is the disturbance phenomenon of physiological AV block. 2, pathological AV block: (1) the influence of vagal tone and the role of drugs can cause AV block, after exercise or the use of atropine drugs can eliminate the influence of vagal tone, significantly improve the function of the AV node, then AV block disappears. Many clinical drugs such as digitalis, calcium antagonists, and central and peripheral sympathetic blockers can cause AV block. (2) Atrioventricular block is more common in acute myocardial infarction than in acute anterior myocardial infarction, and the mechanism of atrioventricular block is related to ischemia and increased vagal tone in this area. Inferior wall myocardial infarction with AV block is often intermittent in character, with normal QRS patterns that may disappear after several days. In acute anterior wall myocardial infarction with type II AV block, the mechanism of the block is related to extensive infarction resulting in the destruction of the conduction bundle branches. Dynamic electrocardiography shows that type II AV block in anterior wall myocardial infarction is often accompanied by intermittent or persistent bundle branch block patterns (left or right bundle branch or branch block patterns). This type of block tends to progress to complete AV block. Patients with first-degree AV block are often asymptomatic and have a diminished apical first heart sound on auscultation. Patients with second degree type I AV block may have pause in heartbeat. Patients with second degree type II AV block often have fatigue, dizziness, fainting, convulsions and cardiac insufficiency, and often develop complete AV block within a short period of time. The symptoms of complete AV block depend on the establishment of ventricular autonomic rhythm and the basic condition of the ventricular rate and myocardium. In patients with bifascicular lesions, the ventricular autonomic rhythm point is very low, and a slow ventricular rate below 40 beats/min can lead to cardiac insufficiency and ischemic syndrome (Adams-Stokes,Syndrome) or sudden death.