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, or if electrical signals don't travel normally through the heart. Many things can cause, an arrhythmia including; scarring of heart tissue, heart disease, high blood pressure, diabetes, overactive thyroid gland, smoking, excessive alcohol or caffeine intake, drug abuse, stress and some medications.
Attribution: Straight Talk Foundation