A resting heart rate of 45 beats per minute may be normal or pathologic and requires a comprehensive analysis. For resting heart rate of 45 beats/min, it can occur in the elderly, who tend to have a slowed heart rate. For pathological factors, such as various organic heart diseases and thyroid abnormalities, the slowed heart rate can be caused. Bradycardia can cause severe states such as blackouts and syncope, and treatment related to permanent cardiac pacing should be given if necessary. In cases of slow resting heart rate, attention is paid to exclude electrolyte disorders, as hypokalemia or hyperkalemia, may cause slowing of the heart rhythm. With a resting heart rate of 45 beats/min, it is recommended to give a 24-hour ambulatory electrocardiogram to clarify the range of their slowest heart rate. If there are long intervals, such as those of 2-3 seconds or more, the possibility of pathological factors is considered to be the main cause.