An arrhythmia (also called dysrhythmia) is an abnormal rhythm of the heart, which can cause the heart to pump less effectively.

Arrhythmias can cause problems with contractions of the heart chambers by:

Not allowing the ventricles (lower chambers) to fill with an adequate amount of blood, because an abnormal electrical signal is causing the heart to pump too fast.

Not allowing a sufficient amount of blood to be pumped out to the body, because an abnormal electrical signal is causing the heart to pump too slowly or too irregularly.

In any of these situations, the heart may not be able to pump an adequate amount of blood to the body with each beat due to the arrhythmia's effects on the heart rate. The effects on the body are often the same, whether the heartbeat is too fast, too slow, or too irregular.