Normal human ECG rhythm is sinus rhythm, heart rate in the normal range of 60-100 beats / min, sinus bradycardia hr55 means sinus rhythm frequency is 55 beats / min. Sinus bradycardia may be seen in physiological and pathological conditions, ① physiological can be seen in healthy young people, athletes and sleep; ② pathological see intracranial disease, severe hypoxia, hypothermia, hypothyroidism, obstructive jaundice, sinus node lesions, lower wall palpitation infarction and the application of certain drugs (such as amiodarone, β-blockers, etc.). Sinus bradycardia hr55 beats/min please go to the hospital, the doctor combined with clinical symptoms, signs and auxiliary examination results to clarify whether it is physiological or pathological, and whether it needs treatment, do not blindly use drugs to avoid delaying the condition.