Causes
Collapse SectionCauses has been expanded.Normally, the chambers of the heart (atria and ventricles) contract in a coordinated manner.The contractions are caused by an electrical signal that begins in an area of the heart called the sinoatrial node (also called the sinus node or SA node).The signal moves through the upper heart chambers (the atria) and tells the atria to contract.After this, the signal moves down in the heart and tells the lower chambers (the ventricles) to contract.