A heart rate of less than 60 beats per minute is called bradycardia. The average resting heart rate is 60 to 100 beats per minute.

Sometimes bradycardia is normal. For example, healthy young adults and well-trained athletes often have resting heart rates of less than 60 beats per minute.

Bradycardia is abnormal when the heart's normal pacemaker does not work correctly or when the normal electrical system of the heart has been damaged. Abnormal bradycardia (also called bradyarrhythmia, sick sinus syndrome, or sinus node dysfunction) is an abnormally slow heart rate that is caused by certain medical conditions—including heart disease, hypothyroidism, and electrolyte imbalances—and some medicines. In severe forms of bradycardia, the heart beats so slowly that it does not pump enough blood to meet the body's needs. This can be life-threatening.

Treatment depends on the condition that is causing it (underlying condition). Bradycardia may go away if the underlying condition can be reversed, such as an electrolyte imbalance. When heart disease is the cause, a pacemaker is often needed to restore a normal heart rate.