A resting heart rate of 55 beats per minute without symptoms is usually normal, but hypothyroidism and sinus node lesions should be excluded. The normal resting heart rate is 60-100 beats per minute. If the heart rate is 55 beats per minute, it is considered bradycardia. If there are no symptoms such as dizziness, blackouts, weakness, or fainting, no treatment is needed, and the slowing of the heart rate is physiologic, and is usually seen in healthy adults and athletes. Hypothyroidism can lead to slow heart rate due to decreased sympathetic excitation; sinus node lesions can lead to slow heart rate due to impaired cardiac pacing signals; and slow heart conduction due to beta-blocking medications can also lead to slow heart rate. When the heart rate slows down, it is necessary to consult a doctor in a timely manner to clarify whether the cause is physiological or pathological, so as to avoid self-diagnosis and delay in the treatment of the condition.