Succinic acid is generally referred to as metoprolol succinate, and it is recommended to reduce the dosage or change the medication under the supervision of a doctor when taking half a tablet a day heart rate 55. Metoprolol succinate is a selective beta 1 receptor blocker, which has the effect of lowering the heart rate, reducing cardiac output and lowering blood pressure. It can be used to treat hypertension, angina pectoris, and stable chronic heart failure. After using the drug often have dizziness, headache, abdominal pain, nausea, vomiting, diarrhea, bradycardia, palpitations and other adverse reactions, some patients can also have arrhythmia, low blood pressure, feeling abnormal and other symptoms. When patients take half a tablet a day, the heart rate of 55, it may be an adverse reaction of bradycardia, it is recommended that patients seek medical attention in a timely manner, according to their own situation to adjust the medication, can be reduced to one-fourth of the dosage or according to the doctor’s advice to change the medication taken. At the same time, we should also pay attention to monitoring the changes in heart rate, if any discomfort in a timely manner to consult the doctor. Such conditions should be treated promptly and in accordance with the doctor’s advice.