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. In Cryptogenic Stroke and Underlying Atrial Fibrillation [CRYSTAL AF], 441 patients randomly assigned to prolonged ambulatory cardiac monitoring with a subcutaneous implantable loop recorder or to a control group with conventional follow- up, detected more AF in the monitored group while in a 30-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation After a Cerebral Ischemic Event: A Randomized Controlled Trial [EMBRACE], 572 patients randomly assigned to additional ambulatory monitoring with a 30-day external loop recorder (intervention group) or a 24-h Holter monitor (control group) found more AF in the intervention group (16.1% vs 3.2% in the control group; In a systematic review and meta-analysis, Sposato described a much higher rate of AF detection after multi-phase sequential cardiac monitoring, at 23.7% (Table 10). 