Bradycardia can be caused by:

• Conditions that damage the heart's electrical system and disrupt the regular, rhythmic impulses that keep the heart rate normal. These conditions include:
  • The aging process. A slow heart rate may develop as a result of age-related changes in the heart.
  • Coronary artery disease.
  • Heart attack.
  • Heart surgery.
  • Myocarditis.
  • Endocarditis.
  • Sarcoidosis.
  • Lyme disease.
• Conditions or medicines that slow the passing of electrical signals through the heart but are not the result of heart damage. These conditions include:
  • Hypothyroidism (underactive thyroid gland).
  • Electrolyte imbalances, such as abnormal blood levels of potassium (hyperkalemia).
  • In some people, certain circumstances, such as standing for a long time, pain, coughing, and vomiting, that stimulate the nervous system and slow the heart rate. The slow heart rate is usually temporary.
  • Heart medicines, such as beta-blockers, calcium channel blockers, antiarrhythmics, and digoxin.