Sleeping with a heart rate of 40-50 beats/minute is generally not dangerous; it is more dangerous if there is other serious discomfort. Adult heart rate, in a quiet state for 60-100 times / min, with the body’s emotional fluctuations, exercise, or hunger, oversatiety and other different states of the body, the heart rate will also have obvious changes. Generally speaking, the human body’s heart rate is in the lowest state when sleeping, at this time the normal people may also appear heart rate 40-50 times / min state. Especially some engaged in heavy labor, often strenuous exercise athletes, etc., due to the heart has a large heart rate reserve, can appear in the sleep 40-50 times / min. If there is no physical discomfort at this time, there is no need for any treatment and there is no danger. However, if there is dizziness, panic, or even fatigue, shortness of breath, fainting, or other physical discomforts, and the heart rate does not exceed 60 beats/minute even under the active state, this indicates that there is a more serious form of bradycardia, which is dangerous and may lead to cardiac arrest. Therefore, if you have a heart rate of 40-50 beats per minute while sleeping, if you have any serious physical discomfort, it is recommended that you consult a doctor in a timely manner and follow the doctor’s instructions for examination and treatment, so as to avoid incorrect medication and damage to the body.