Normal heart rate is between 60 and 100 beats per minute. Arrhythmia is a medical term that refers to a heart rate that is outside of this normal range. An arrhythmia that is too slow is called a bradyarrhythmia or bradycardia.
When the heart is beating under 60 beats per minute, this is refered to as Bradycardia . While in some people this can be a sign of a possible condition it is also important to note that some people with healthy hearts may have a heart rate below 60 beats per minute (bpm). Many well conditioned atheletes have heart rates at rest below 60bpm. Some individuals may have heart rates that fall below 60bpm while sleeping.
The two most common causes of bradycardia are diseases of the sinoatrial (SA) node (sick sinus syndrome), which is the heart’s natural pacemaker or other problems with the heart’s electrical conduction system (heart block). These diseases can cause the heart to beat too slowly all the time or occasionally. In either case, the heart may not pump enough blood to meet the body’s needs. As the heart rate declines, there is not sufficient blood flow to the brain, causing feelings of light-headedness, and sometimes, fainting.
Every normal heart has a normal rhythm. That rhythm varies from person to person. In most healthy people, the heart at rest beats about 60 to 100 times per minute. A small bunch of heart cells called the sinoatrial node keeps time.