Men and women age 65 and older are most likely to develop a slow heart rate that needs treatment. As a person ages, the electrical system of the heart often does not function normally. The decline in heart function may be caused by the accumulation of fibrous tissue in the heart. This excess tissue may interfere with how the heart's electrical system works and cause a slow heart rate.

People with very healthy hearts, such as athletes, often have a slower heart rate than the average of 60 to 100 beats per minute. These slower heart rates reflect a healthy heart that is in good condition, and they are not likely to cause symptoms.