The most significant manifestation of first-degree AV block on the ECG is a PR interval of more than 210 ms. It has two prerequisites, one is in sinus rhythm, that is, the P-wave in lead II must be positive, the aVR lead is inverted, if there is a leftward deviation of the P-wave electric axis, the P-wave in lead II may not be very clear, there are two ways to deal with this, one is to increase the machine voltage to twice, that is, 20 MV. The P wave in lead I is positive, but it is possible that the P wave axis is left-skewed, causing the P wave in lead II to be low or small, so this is the time to pay attention to the identification. The second premise is to pay attention to the distinction between atrioventricular separation, that is, in this case, the relationship between P waves and QRS wave groups is 1:1 conduction, a P wave followed by a QRS wave group, if the PR interval is more than 210 ms, one degree of AV block, in the clinic there are physiological and pathological. In physiological cases, some people may have chest tightness or even chest pain radiating to the left upper extremity, which may be caused by exertion, lack of sleep or anxiety, etc. The PR interval may be normal. The most common pathological condition is inferior wall myocardial infarction, in which myocardial ischemia affects the blood supply to the sinus node, so that atrioventricular block occurs for a time. Another noteworthy condition is first-degree AV block with a prolonged PR interval. In this case, atrioventricular conduction is not synchronized, that is, the atria and ventricles do not beat in the same way. The patient may have headache, headache, cerebral hypoperfusion, etc., or myocardial ischemia, i.e., multiple organ ischemia, for example, the patient is very uncomfortable, but other tests may be normal in the early stage, and only the ECG shows prolonged PR interval. In other words, the clinical findings are very mild, but the clinical symptoms are very severe and the consequences are very serious, and the patient may sometimes cause sudden death, which can only be completely solved by installing a pacemaker.