Background ST elevation (STE) on the electrocardiogram (ECG) may be due to acute myocardial infarction (AMI) or other nonischemic pathologies such as left ventricular aneurysm (LVA). The objective of this study was to validate 2 previously derived ECG rules to distinguish AMI from LVA. The first rule states that if the sum of T-wave amplitudes in leads V1 to V4 divided by the sum of QRS amplitudes in leads V1 to V4 is greater than 0.22, then acute ST-segment elevation MI is predicted. The second rule states that if any 1 lead (V1-V4) has a T-wave amplitude to QRS amplitude ratio greater than or equal to 0.36, then acute ST-segment elevation MI is predicted. Methods This was a retrospective analysis of patients with AMI (n = 59) and LVA (n = 16) who presented with ischemic symptoms and STE on the ECG. For each ECG, the T-wave amplitude and QRS amplitude in leads V1 to V4 were measured. These measurements were applied to the 2 ECG rules; and sensitivity, specificity, and accuracy in predicting AMI vs LVA were calculated. Results For rule 1 (sum of ratios in V1-V4), sensitivity was 91.5%, specificity was 68.8%, and accuracy was 86.7% in predicting AMI. For rule 2 (maximum ratio in V1-V4), sensitivity was 91.5%, specificity was 81.3%, and accuracy was 89.3% in predicting AMI. Conclusions When patients present to the emergency department with ischemic symptoms and the differential diagnosis for STE on the ECG is AMI vs LVA, these 2 ECG rules may be helpful in differentiating these 2 pathologies. Both rules are highly sensitive and accurate in predicting AMI vs LVA.