In second degree sinus atrioventricular block, including second degree type I sinus atrioventricular block and second degree type II sinus atrioventricular block, second degree type I sinus atrioventricular block has an incremental sinus interval, often with a gradual change in the P-R interval until the QRS waves fall off, and second degree type II sinus atrioventricular block has a sudden fall off of the QRS waves. In this case, it is usually necessary to actively search for the cause and treat the cause. In the case of a high degree of sinus conduction block, the patient may experience dizziness, syncope or even loss of consciousness, and in severe cases, permanent pacemaker implantation is required. In general, the main drugs used for sinus block are atropine and isoproterenol.