A Surprisingly, the symptoms of a heart rate that's too fast or too slow are very similar, because in both situations the end result is an insufficient amount of blood reaching the vital organs, such as the brain. People with very slow heart rates have trouble exercising and may feel fatigued or short of breath. If the heart actually stops or if the rate is too slow to sustain the vital organs, sudden death can result.
People feel dizzy or lightheaded and can faint.
Like those with slow heart rates, people with very fast heart rates may also have difficulty with exercise. They may feel short of breath or fatigued. Medications, electronic devices and electrosurgery are the main treatments. Cardiac arrhythmias, particularly bradyarrhythmias due to conduction blocks, are among the most treatable of medical disorders. In neuromuscular disorders, the first step is often to assess the cause of the abnormal heart rate or rhythm and determine whether or not the conduction system itself is the primary problem.