2025 ICD-10-CM Diagnosis Code I21.3

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ST elevation (STEMI) myocardial infarction of unspecified site

  • I21.3 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
  • Short description: ST elevation (STEMI) myocardial infarction of unsp site
  • The 2025 edition of ICD-10-CM I21.3 became effective on October 1, 2024.
  • This is the American ICD-10-CM version of I21.3 – other international versions of ICD-10 I21.3 may differ.

Applicable To

  • Acute transmural myocardial infarction of unspecified site
  • Transmural (Q wave) myocardial infarction NOS
  • Type 1 ST elevation myocardial infarction of unspecified site

The following code(s) above I21.3 contain annotation back-references

 that may be applicable to I21.3:

  • I00-I99  Diseases of the circulatory system
  • I20-I25  Ischemic heart diseases
  • I21  Acute myocardial infarction

Approximate Synonyms

  • Acute heart attack
  • Acute myocardial infarction
  • Acute myocardial infarction due to occlusion of left coronary artery
  • Acute st segment elevation myocardial infarction
  • Atrial septal defect after acute heart attack
  • Atrial septal defect as current complication following acute myocardial infarction
  • Chordae tendineae rupture after acute heart attack
  • Heart attack, acute
  • Heart attack, less than 8 weeks ago
  • Hemopericardium after acute heart attack
  • Hemopericardium as current complication following acute myocardial infarction
  • History of myocardial infarction less than 4 weeks ago
  • Hx of mi, < 8 weeks
  • Mi acute st segment elevation
  • Mural thrombus of heart, following heart attack
  • Myocardial infarction (heart attack)
  • Myocardial infarction (heart attack), < 4weeks
  • Post-infarction mural thrombus
  • Rupture of chordae tendinae as current complication following acute myocardial infarction
  • Rupture of interventricular septum
  • Rupture of interventricular septum following acute myocardial infarction
  • Rupture of papillary muscle as current complication following acute myocardial infarction
  • Rupture papillary muscle complicating acute heart attack
  • Subsequent heart attack, anterior wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, anterolateral wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, inferior wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, inferolateral wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, inferoposterior wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, posterior wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, posterolateral wall, within 4 weeks of previous heart attack
  • Subsequent heart attack, within 4 weeks of previous heart attack
  • Subsequent non-st elevation myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation anterior wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation anterolateral wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation inferior wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation inferolateral wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation inferoposterior wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation posterior wall myocardial infarction, within 4 weeks of previous myocardial infarction
  • Subsequent st elevation posterolateral wall myocardial infarction, within 4 weeks of previous myocardial infarction

Clinical Information

  • Necrosis of the myocardium, as a result of interruption of the blood supply to the area. It is characterized by a severe and rapid onset of symptoms that may include chest pain, often radiating to the left arm and left side of the neck, dyspnea, sweating, and palpitations.

ICD-10-CM I21.3 is grouped within Diagnostic Related Group(s) (MS-DRG v42.0):

  • 280 Acute myocardial infarction, discharged alive with mcc
  • 281 Acute myocardial infarction, discharged alive with cc
  • 282 Acute myocardial infarction, discharged alive without cc/mcc
  • 283 Acute myocardial infarction, expired with mcc
  • 284 Acute myocardial infarction, expired with cc
  • 285 Acute myocardial infarction, expired without cc/mcc

Convert I21.3 to ICD-9-CMCode History

  • 2016 (effective 10/1/2015): New code (first year of non-draft ICD-10-CM)
  • 2017 (effective 10/1/2016): No change
  • 2018 (effective 10/1/2017): No change
  • 2019 (effective 10/1/2018): No change
  • 2020 (effective 10/1/2019): No change
  • 2021 (effective 10/1/2020): No change
  • 2022 (effective 10/1/2021): No change
  • 2023 (effective 10/1/2022): No change
  • 2024 (effective 10/1/2023): No change
  • 2025 (effective 10/1/2024): No change

Diagnosis Index entries containing back-references to I21.3:

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