Atrial flutter is a macro-reentrant circuit arrhythmia, most commonly involving a counterclockwise loop through the cavotricuspid isthmus (CTI) in the right atrium — termed typical or CTI-dependent flutter. The atrial rate is characteristically regular at 250–350 bpm (most commonly ~300 bpm). Because the AV node cannot conduct all impulses, a fixed or variable conduction ratio occurs: 2:1 block is most common (ventricular rate ~150 bpm), but 3:1, 4:1, or variable block can occur. The sawtooth or 'picket fence' flutter waves (F waves) are best seen in leads II, III, aVF, and V1. Unlike AFib, atrial flutter involves a single organized circuit rather than chaotic multifocal activity. Atypical flutter involves circuits outside the CTI (left atrium, scarred tissue from prior ablation or surgery) and may not display classic sawtooth morphology. Atrial flutter often coexists with or degenerates into AFib. The organized atrial contraction in flutter is mechanically ineffective due to the rapid rate, and similar to AFib, stasis in the left atrial appendage can occur — stroke risk and anticoagulation guidelines parallel those for AFib.