Atrioventricular block is a blockage of impulses during atrioventricular conduction. There are two types of block: incomplete and complete. The former includes first- and second-degree AV block, while the latter is also called third-degree AV block, and the block can be in the atrium, AV node, Hitchcock’s bundle and double bundle branches. In complete AV block, the temporal relationship between the atria and the ventricles is separated, and the atria lose their auxiliary pumping effect on ventricular contraction, resulting in a decrease in cardiac output. Electrocardiographic examination of the loss of the auxiliary pumping effect of atria on ventricular contraction: 1. 1st degree AV block (1) Sinus P waves are followed by QRS wave groups. (2) Prolonged P-R interval: P-R interval ≥0.21s (>0.22s in elderly). 2.Second-degree AV block (1) Second-degree type I is also called Mohs type I or Wen type. The electrocardiogram shows that: (1) the P wave appears regularly; (2) the P-R interval is progressively prolonged (while the R-R interval is progressively shortened) until a ventricular leak occurs, after which the P-R interval returns to the shortest, and then gradually prolongs until another ventricular leak occurs. This cycle is referred to as the ventromedial phenomenon of atrioventricular conduction. The ratio of atrioventricular conduction is often 3:2, 4:3, 5:4, etc. (2) Degree II type II is also called Mohs type II. The electrocardiogram shows regular P waves, constant P-R intervals (normal range or prolonged) for all downward transmitted beats before and after the occurrence of a missed ventricular beat, proportional dehiscence of QRS wave groups, and generally normal or widened deformities in morphology. The atrioventricular conduction ratio is often 2:1, 3:2, 4:3, etc. (1) There is no fixed relationship between P wave and QRS wave group, and the P-P and R-R spacing have their own fixed regularity. (2) Atrial rate > ventricular rate, that is, the P wave frequency is higher than the QRS wave group frequency. (3) The QRS wave group pattern is normal or wide and deformed.