There is some danger of having a heart rate of around 40 beats per minute, and if this condition persists for a longer period of time, the danger may be greater. The average adult heart rate is around 60-100 beats per minute, and a heart rate of only 40 beats per minute indicates a slow heartbeat. A slow heart rate may lead to low blood ejection from the heart, and several parts of the body and organs may not get enough blood supply. In mild cases, the symptoms may be dizziness, headache, weakness and panic, but in severe cases, the slow heart rate may cause fainting and shock. If the blood supply to internal organs such as kidneys and liver is insufficient, it will lead to the organ function being affected. And once the liver and kidneys have problems, it will in turn affect the heart function. Therefore, a heart rate of 40 beats per minute for a long period of time may cause more serious harm and must be given high priority. In addition, once the heart rate is low to about 40 beats/min, it is recommended to go to the hospital for an ambulatory electrocardiogram examination in a timely manner and under the guidance of a doctor for treatment. However, if a transient low heart rate of 40 beats/min occurs during sleep and there are no uncomfortable symptoms, observation may continue.