Cardiovascular causes of syncope fall into two main categories, arrhythmia (e.g. ventricular tachycardia (VT), 2nd degree Mobitz II, 3rd degree atrioventricular block or symptomatic bradycardia) and structural (e.g. aortic stenosis). It is arrhythmia that is most difficult for the ED clinician to diagnose in the ED as examination and presenting Electrocardiogram ECG may both be normal. It is for this reason that arrhythmia makes up a large number of subsequent serious outcomes in syncope patients whose syncopal cause is unexplained after ED assessment.