Arrhythmias are very common, both the harmless type and the dangerous type. An arrhythmia can be caused by:

  • The heart's natural pacemaker developing an abnormal rate or rhythm
  • The normal electrical conduction pathway being interrupted by injury, illness, or electricity
  • Another part of the heart (other than the sinus node) taking over as pacemaker

The most common cause of dangerous arrhythmias is a heart attack. When the heart is deprived of adequate blood supply during a heart attack, its electrical activity can become erratic. Diseased heart valves and diseased heart muscle, direct injury to the heart, diseases that alter the body's chemical balance, and several kinds of medication can also upset the heart's circuitry.

The most common causes of arrhythmia include:

  • Coronary artery disease (eg, heart attacks)
  • Diseased myocardium (heart muscle)
  • Abnormal heart valves
  • Electrolyte abnormalities
  • Birth defects
  • Stress
  • Caffeine
  • Tobacco
  • Alcohol
  • Illegal stimulants, such as cocaine and methedrine
  • Diet pills
  • Some over-the-counter medications, such as cough and cold medicines
  • Various prescription medications, for example:
    • Heart medicines
    • Asthma medicines
    • Psychoactive medicines, such as antidepressants
    • Thyroid hormone replacement medicines