ESUS has been de ned as ischemic stroke detected by CT or MRI that, after a standardized and adequate diagnostic pathway including brain imaging, echocardiography, cardiac rhythm monitoring for at least 24 h, and imaging of the intracranial and extracranial arteries supplying the affected brain area: is not lacunar (subcortical, < 15 mm diameter); where there is absence of extracranial or intracranial atherosclerosis causing $ 50% luminal stenosis in the arteries supplying the area of ischemia; no major-risk cardioembolic source of embolism (permanent or paroxysmal AF, sustained atrial utter, intra-cardiac thrombus, prosthetic cardiac valve, atrial myxoma or other cardiac tumours, mitral stenosis, recent [< 4 weeks] MI, left ventricular ejection fraction < 30%, valvular vegetations, or infective endocarditis); and no other speci c cause of stroke identi ed (eg, arteritis, dissection, migraine/vasospasm, Thus, ESUS is a subcategory of cryptogenic stroke, accounting for about 1 in 6 ischemic strokes.357 A careful and systematic diagnostic workup in patients with ESUS is needed as there might be important management differences between underlying embolic sources if detected, such as aortic arch atheroma, patent foramen ovale, and paroxysmal AF. This brief section only refers to the latter. As a general principle, AF can be detected in a high proportion of ESUS patients, if we look harder, look longer and look with more sophisticated monitoring Screening consecutive patients with ischemic stroke with routine Holter or event loop recorder monitoring will identify new AF/atrial utter in Two RCTs clearly showed that prolonged cardiac monitoring increases the detection of occult AF in patients with TIA or acute ischemic stroke presenting in sinus rhythm. 