An arrhythmia can occur if the electrical signals that control the heartbeat are delayed or blocked. This can happen if the special nerve cells that produce electrical signals don't work properly. It also can happen if the electrical signals don't travel normally through the heart.
An arrhythmia also can occur if another part of the heart starts to produce electrical signals. This adds to the signals from the special nerve cells and disrupts the normal heartbeat.
Smoking, heavy alcohol use, use of some drugs (such as cocaine or amphetamines), use of some prescription or over-the-counter medicines, or too much caffeine or nicotine can lead to arrhythmias in some people.
Strong emotional stress or anger can make the heart work harder, raise blood pressure, and release stress hormones. Sometimes these reactions can lead to arrhythmias.
A heart attack or other condition that damages the heart's electrical system also can cause arrhythmias. Examples of such conditions include high blood pressure, coronary heart disease, heart failure, an overactive or underactive thyroid gland (too much or too little thyroid hormone produced), and rheumatic heart disease.
Congenital (kon-JEN-ih-tal) heart defects can cause some arrhythmias, such as Wolff-Parkinson-White syndrome. The term "congenital” means the defect is present at birth.
Sometimes the cause of arrhythmias is unknown.