A heart rate of 40-50 beats/min during sleep indicates a low heart rate and may be abnormal, further examination is recommended. Normal adults generally have a heart rate of 60-100 beats/minute when awake, but the heart rate will be slow during sleep, when metabolism and sympathetic excitability are at a low level. The heart rate during sleep is typically 50-70 beats/min for men and 60-70 beats/min for women. If the patient has bradycardia, the heart rate during sleep may be only 40 beats/min or even lower. In this case, a 24-hour ambulatory electrocardiogram is recommended to further clarify whether there is any abnormality in heart function, identify the cause and do targeted treatment. Generally, asymptomatic sinus bradycardia can be treated without treatment. If patients have symptoms of insufficient cardiac output, they can be treated with atropine, isoprenaline and other drugs as prescribed by the doctor.