The ECG findings of an acute posterior wall MI include the following: ST segment depression (not elevation) in the septal and anterior precordial leads (V1-V4). This occurs because these ECG leads will see the MI backwards; the leads are placed anteriorly, but the myocardial injury is posterior. A R/S wave ratio greater than 1 in leads V1 or V2. ST elevation in the posterior leads of a posterior ECG (leads V7-V9). Suspicion for a posterior MI must remain high, especially if inferior ST segment elevation is also present. ST segment elevation in the inferior leads (II, III and aVF) if an inferior MI is also present T wave inversion(V1-V6) is also present Ref Davidson edition23rd pg 463