A heartbeat of 105 beats/minute in a quiet state in a 13-year-old boy is usually considered abnormal. However, the heartbeat may also go up to 105 beats per minute in cases of exercise or emotional excitement, which is usually normal and will be relieved by rest. The speed of the heartbeat is influenced by multiple factors; it is faster during activity than when it is quiet, and it may slow down significantly when you fall asleep quietly at 2-3 am. If a 13-year-old boy’s heart rate of 105 beats per minute only occurs during strenuous exercise or emotional stress, it is mostly a normal phenomenon, and the heart rate can return to normal after resting and quiet time. However, if the heartbeat does not slow down and return to normal, or if the heartbeat is 105 beats per minute for several times, the heartbeat may be abnormally fast. There are many conditions that can cause a fast heartbeat, such as anemia, hyperthyroidism, or problems with the heart itself. If a 13-year-old boy’s heartbeat is 105 beats per minute and his symptoms are not relieved, or accompanied by other symptoms, it is recommended to consult a doctor in a timely manner to clarify the cause of the disease and then carry out targeted treatment.