An '''arrhythmia''' is any disorder of a person's [[heart]] rate or rhythm. Their heart beats too quickly, too slowly or with an irregular pattern. When the heart beats faster than normal, it is called '''tachycardia'''. When the heart beats too slowly, it is called '''bradycardia'''.
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Many factors can affect the heart's rhythm, such as having a heart attack, blood chemistry imbalances or abnormal hormone levels. Some substances or medicines may also cause arrhythmias.