2026 ICD-10-CM Diagnosis Code I21.4Non-ST elevation (NSTEMI) myocardial infarction

ICD-10-CM Codes›I00–I99›I20-I25›I21

ICD-10-CM I21.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I21.4 is a billable ICD-10-CM diagnosis code for Non-ST elevation (NSTEMI) myocardial infarction. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 280 through 285. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acute myocardial infarction.

This medical diagnosis code is frequently used in Cardiology medical specialties to designate conditions such selected atherosclerosis, ischemia, and infarction.

Code Identity

ICD-10-CM Code
I21.4
Billable Status
Yes — Valid for Submission
Code Describes
Non-ST elevation (NSTEMI) myocardial infarction
Short Description
Non-ST elevation (NSTEMI) myocardial infarction
Same as the full description in the CMS dataset.
Parent Code
I21
Acute myocardial infarction

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI20-I25Ischemic heart diseases
CategoryI21Acute myocardial infarction
This CodeI21.4Non-ST elevation (NSTEMI) myocardial infarction

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute anterior non-ST segment elevation myocardial infarction
  • Acute anterior non-ST segment elevation myocardial infarction with right ventricular involvement
  • Acute anteroseptal myocardial infarction
  • Acute inferior non-ST segment elevation myocardial infarction
  • Acute inferior non-ST segment elevation myocardial infarction of right ventricle
  • Acute myocardial infarction of anterior wall involving right ventricle
  • Acute myocardial infarction of anterolateral wall
  • Acute myocardial infarction of inferior wall
  • Acute myocardial infarction of inferolateral wall
  • Acute myocardial infarction of right ventricle
  • Acute non-Q wave infarction
  • Acute non-Q wave infarction - anterolateral
  • Acute non-Q wave infarction - anteroseptal
  • Acute non-Q wave infarction - inferior
  • Acute non-Q wave infarction - inferolateral
  • Acute non-Q wave infarction - lateral
  • Acute non-Q wave infarction - widespread
  • Acute non-ST segment elevation myocardial infarction
  • Acute non-ST segment elevation myocardial infarction of right ventricle
  • Acute subendocardial infarction
  • Acute widespread myocardial infarction
  • EKG: myocardial infarction
  • EKG: subendocardial infarct
  • Non-Q wave myocardial infarction
  • Postoperative myocardial infarction
  • Postoperative subendocardial myocardial infarction
  • Subendocardial myocardial infarction

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Acute subendocardial myocardial infarction
  • Non-Q wave myocardial infarction NOS
  • Nontransmural myocardial infarction NOS
  • Type 1 non-ST elevation myocardial infarction

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • non-Q wave
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • non-ST elevation (NSTEMI)
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • nontransmural
    • Infarct, infarction
      • nontransmural
    • Infarct, infarction
      • subendocardial (acute) (nontransmural)
    • Necrosis, necrotic(ischemic)
      • subendocardial (acute)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR CIR009
Acute myocardial infarction
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Acute Myocardial Infarction

    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.

  • Acute Myocardial Infarction by ECG Finding|ACUTE MYOCARDIAL INFARCTION|Acute Myocardial Infarction|Acute Myocardial Infarction by EKG Finding

    an electrocardiographic finding showing a current of injury with st elevation. no specification is provided for localization. (cdisc)

  • Acute Myocardial Infarction From PCI Complication Type|PCI Acute Angiographic Complication|PCI Acute Angiographic Complication|PCI Acute Angiographic Complication|PCIAAC|PCIAAC

    a description of the complications from a percutaneous coronary intervention procedure that lead to an acute myocardial ischemic event.

  • Acute Myocardial Infarction Type|ACMITYPE|ACMITYPE

    a classification or description of the acute myocardial infarction.

  • Death due to Acute Myocardial Infarction Related to COVID-19|Death due to acute MI

    death by any cardiovascular mechanism (e.g., arrhythmia, sudden death, heart failure (hf), stroke, pulmonary embolus, peripheral arterial disease) less than or equal to 30 days after a myocardial infarction (mi), related to the immediate consequences of the mi, such as progressive hf or recalcitrant arrhythmia in a patient with probable or confirmed acute covid-19.

  • Acute Myocardial Infarction by ECG Finding|ACUTE MYOCARDIAL INFARCTION|Acute Myocardial Infarction|Acute Myocardial Infarction by EKG Finding

    an electrocardiographic finding showing a current injury of the myocardium.

Patient EducationClinical

Heart Attack

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Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert I21.4 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
410.71 Subendo infarct, initial
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About I21.4Overview

Is I21.4 (Acute myocardial infarction) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report Non-ST elevation (NSTEMI) myocardial infarction on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does I21.4 group to?

When Non-ST elevation (NSTEMI) myocardial infarction is the principal diagnosis on an inpatient stay, it groups to MS-DRG 280, 281, 282, 283, 284, 285, with relative weights from 0.5989 to 1.9808 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of I21.4?

Under the General Equivalence Mappings, Non-ST elevation (NSTEMI) myocardial infarction converts to ICD-9-CM 410.71 (subendo infarct, initial). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.