The risk of getting an arrhythmia varies depending on:

• Blood chemistry imbalances, such as abnormal potassium levels
• Cardiomyopathy a weakening of the heart muscle or a change in the heart muscle
• Heart failure
• Overactive thyroid gland
• Heart attack
• High blood pressure
• Coronary heart disease
• rheumatic heart disease

Some substances or drugs may also cause arrhythmias:

• Amphetamines
• Smoking
• Caffeine
• Cocaine
• Beta blockers
• Psychotropics
• Sympathomimetics
• Anti-arrhythmic medications prescribed to treat one type of arrhythmia can sometimes cause another type of arrhythmia

Congenital heart defects can also cause some arrhythmias. "Congenital," means that the defect is present at birth. An example is Wolff-Parkinson-White syndrome.

The cause of an arrhythmia can also be unknown.