Bradycardia is a heart rate of less than 60 beats per minute. A slow heart rate does not automatically cause adverse symptoms and may not require treatment, according to the American Heart Association.
An electrical system that signals the heart muscle to contract and pump blood to the rest of the body controls the heartbeat. Bradycardia happens when these signals are blocked or slowed, explains the Heart Rhythm Society. The problem may reside in the heart's natural pacemaker, the sinus node, as it wears down over time and fails to fire off signals. Alternately, an individual suffering from bradycardia may experience a fraying or breakage of the wires that conduct electrical signals to the heart muscle. In this case, the sinus node fires normally, but the signal to squeeze does not reach the muscle.
A heart rhythm that is too slow can cause insufficient blood flow to the brain with symptoms such as fatigue, dizziness, lightheadedness, fainting, and in extreme cases, cardiac arrest. Bradycardia that goes untreated may lead to heart failure, loss of consciousness, chest pain or high blood pressure, warns the American Heart Association. An artificial pacemaker, which speeds up the heart when it slows down, can usually correct the condition.