Macro-reentrant atrial tachycardias, also called “atypical” atrial flutters resuts from atrial fibrosis or from scars secondary to previous catheter or surgical ablation. 1-2. Previous reports have documented that a dual loop figure-8 reentrant atrial tachycardia can occurr utilizing a common critical isthmus. The present report describes the use of high density mapping with a multielectrode grid catheter that enabled the identification of an isthmus of slow conduction shared by two different reentrant circuits. The first radiofrecuency application regularized the cycle length of the tachycardia that was terminated by interrupting conduction at the isthmus.