Editing Heart (section)

==== Cardiac arrhythmias ====<!-- Abnormalities of rhythm-->
{{main|Arrhythmia}}
{{Listen|filename=|title=An irregular heartbeat|description=Recording of heart sounds from a 16-year-old girl with a cardiac arrhythmia.|pos=[[wav]]}}
While in the healthy heart, waves of electrical impulses originate in the [[Sinoatrial node|sinus node]] before spreading to the rest of the atria, the [[atrioventricular node]], and finally the ventricles (referred to as a [[Sinus rhythm|normal sinus rhythm]]), this normal rhythm can be disrupted. Abnormal heart rhythms or arrhythmias may be asymptomatic or may cause palpitations, blackouts, or breathlessness. Some types of arrhythmia such as [[atrial fibrillation]] increase the long term risk of [[stroke]].<ref name=":3" />

Some arrhythmias cause the heart to beat abnormally slowly, referred to as a [[bradycardia]] or bradyarrhythmia. This may be caused by an [[Sick sinus syndrome|abnormally slow sinus node]] or damage within the cardiac conduction system ([[heart block]]).<ref name=":1" /> In other arrhythmias the heart may beat abnormally rapidly, referred to as a [[tachycardia]] or tachyarrhythmia. These arrhythmias can take many forms and can originate from different structures within the heart—some arise from the atria (e.g. [[atrial flutter]]), some from the atrioventricular node (e.g. [[AV nodal reentrant tachycardia|AV nodal re-entrant tachycardia]]) whilst others arise from the ventricles (e.g. [[ventricular tachycardia]]). Some tachyarrhythmias are caused by scarring within the heart (e.g. some forms of [[ventricular tachycardia]]), others by an irritable focus (e.g. focal [[atrial tachycardia]]), while others are caused by additional abnormal conduction tissue that has been present since birth (e.g. [[Wolff–Parkinson–White syndrome|Wolff-Parkinson-White syndrome]]). The most dangerous form of heart racing is [[ventricular fibrillation]], in which the ventricles quiver rather than contract, and which if untreated is rapidly fatal.<ref>{{Cite journal|last1=Blomström-Lundqvist|first1=Carina|last2=Scheinman|first2=Melvin M.|last3=Aliot|first3=Etienne M.|last4=Alpert|first4=Joseph S.|last5=Calkins|first5=Hugh|last6=Camm|first6=A. John|last7=Campbell|first7=W. Barton|last8=Haines|first8=David E.|last9=Kuck|first9=Karl H.|date=2003-10-14|title=ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias – executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Supraventricular Arrhythmias)|journal=Circulation|volume=108|issue=15|pages=1871–1909|doi=10.1161/01.CIR.0000091380.04100.84|issn=1524-4539|pmid=14557344|doi-access=free}}</ref>