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Background The lateral left atrium (LA) is often associated with atrial tachycardia (AT) because of its complex anatomy. We sought to characterize ATs associated with the lateral LA, including the posterolateral mitral isthmus (MI) and left atrial ridge. Methods and Results Twenty‐eight lateral LA‐associated ATs were mapped with high‐resolution mapping systems and entrainment pacing. The vein of Marshall was mapped with a 1.8‐Fr mapping catheter when possible. ATs were associated with the posterolateral MI in 18 ATs (14 perimitral, 3 small reentry, and 1 focal AT). All patients had undergone MI area ablation, and all ATs were successfully eliminated. During 27.0 (interquartile range, 10.5–40.0) months of follow‐up, all were free from any atrial tachyarrhythmias, with 3 patients on antiarrhythmics. Of 10 ATs involving the ridge or Marshall bundle, 3 were ridge related, 3 were Marshall bundle related based on vein of Marshall mapping, and 1 was a persistent left superior vena cava related AT. All 7 patients had undergone MI linear ablation. The critical isthmus was in the LA‐ridge junction or the LA‐Marshall bundle junction. Bidirectional conduction block between the LA and ridge or Marshall bundle was created. Two patients had the critical isthmus in the other area. The remaining patient had micro‐reentry in the ridge. All 10 ATs were terminated during ablation at the critical isthmus. During 12.0 (5.2–31.7) months of follow‐up, all were free from any atrial tachyarrhythmias, with 7 patients on antiarrhythmics. Conclusions Most ATs occurred after MI area ablation. An high resolution mapping‐guided approach is highly effective for identifying the mechanism.