The various stages of myocardial infarction are classified using aspects of their electropathophysiologic evolution, international nomenclature, histopathologic evolution, as well as common clinical findings and clinical experiences.

The usual nomenclature emphasizes chronology (onset of symptoms). The usual nomenclature differs from international nomenclature.

1. Acute Stage
   • Marked ST elevation (> 3 mm, up to 12 mm) representing transmural injury
2. Subacute Stage
   • Moderate ST elevation with Q waves or QS waves representing minor injury with tissue necrosis 
   • Symmetric, negative T waves, representing ischemia
3. Chronic Stage 
   • A classical Q wave pattern of > 0.04 seconds or a QS wave followed by an isoelectric ST segment
   • A normal or negative T wave

International nomenclature combines the subacute stage with the chronic stage of MI. This text adheres to international nomenclature, which is standard practice in the US.