Which leads show lateral MI?

• A. ST elevation in I, aVL, V5-V6; reciprocal depression in inferior leads
• B. ST elevation in II, III, aVF
• C. ST elevation in V1-V3
• D. ST depression in V7-V9

Answer: (A)

Lateral myocardial infarction shows injury patterns on the ECG that come from the lateral wall of the left ventricle, so the leads that view that area—typically I, aVL, and V5-V6—show ST elevation. The accompanying reciprocal change is often seen as ST depression in the inferior leads (II, III, aVF), which helps confirm the lateral territory involvement and reflects the heart’s vector moving away from those inferior leads.

This pattern is distinct from other territory MIs: inferior MI produces ST elevation in II, III, and aVF; anterior/septal MI produces ST elevation in V1-V3; posterior MI can present with ST depression in V1-V3 (and may show posterior leads like V7-V9 with changes).