The side effects of betalac are mainly in the following aspects: first, slowing down the heart rate, if the patient has bradycardia, such as hypertension with bradycardia, it is not recommended to take betalac to lower blood pressure; second, causing bronchospasm, for example, some patients in the acute phase of asthma taking this drug will aggravate asthma; third, reducing myocardial contractility, the acute phase of heart failure is not recommended to take betalac, may worsen the heart function; fourth, aggravating atrioventricular block, for example, some patients have second degree type II or higher atrioventricular block. Fourthly, it may aggravate the atrioventricular block, for example, some patients have second degree type II or above atrioventricular block, if they take betalac, it may become high or third degree atrioventricular block, which will seriously affect the function of the heart, and the patients may have symptoms such as blackness, chest tightness, dizziness and fainting.