Atrial flutter (AFL) is usually associated with a fixed ratio AV block. If there is 1:1 conduction, the ventricular rates will be very high. A typical situation of AFL is with 2:1 conduction, atrial rate of 300/min and ventricular rate of 150/min. Hence a narrow QRS tachycardia with a rate of 150/min, which appears to be SVT is likely to be atrial flutter with 2:1 conduction. Hence a close scrutiny of the baseline for saw-tooth like flutter waves, especially in the inferior leads is needed to exclude atrial flutter. Since AFL is due to a macro-reentry, it is the arrhythmia which is most sensitive to cardioversion at low energies. Carotid sinus massage is useful in bringing out a diagnosis of AFL because the increase in the grade of AV block makes the flutter waves more evident. Similar effect can be obtained with adenosine as mentioned above.