This webinar aims to improve technologist knowledge and confidence in ECG recognition. The webinar reviews the basic electrophysiology of the cardiac conduction system and how this system normally manifests on ECG. This review is followed by a basic discussion on the underlying pathophysiology of atrial and ventricular arrhythmias which are commonly encountered on polysomnography. Key points for recognition of these arrhythmias on ECG are highlighted throughout the discussion and reinforced through case based discussion from examples on polysomnography.