A nocturnal heart rate of less than 50 beats per minute is normal if there are no symptoms such as panic or chest tightness, or if it has been at this level for a long time. The normal resting heart rate for the average adult during waking hours is 60-100 beats per minute, with an average of 75 beats per minute. To determine whether a particular heart rate value is normal, you can look at it in two ways: 1. If you are asleep at night, your heart rate will be a little lower compared to the daytime because your metabolism is lower. So if there are no other symptoms of cardiovascular disease, it is usually normal. 2. Heart rate in the long-term adaptive state can also occur in the quiet when the heart rate is slow, such as athletes resting heart rate level tends to be lower, which is a kind of adaptive function of good performance. Therefore, if you have a daily exercise habit, long-term monitoring and measurement of heart rate are 50 beats per minute level, do not worry about abnormal. In summary, the nighttime heart rate is lower than 50 beats / minute, first of all, to see whether they have regular exercise habits, usually have chest tightness, chest pain and other symptoms, if in line with the adaptive characteristics of athletes, no adverse symptoms do not need to worry too much, on the contrary, we need to do further examination, so as to determine the exact disease.