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I21 ICD-10-CM Code: Acute myocardial infarction

Billing Status: NO. This is a clinician non-billable / parent hierarchy grouping in the ICD-10-CM system.

Coding at a Glance

Tabular directives
7 inclusion terms · 3 Excludes2 · 7 use-additional codes · 1 code-also instruction

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for I21 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on I21 itself; “inherited from” names the category or block whose note applies here.

Includes

Conditions the official ICD-10-CM tabular list includes under this code.

  • cardiac infarction
  • coronary (artery) embolism
  • coronary (artery) occlusion
  • coronary (artery) rupture
  • coronary (artery) thrombosis
  • infarction of heart, myocardium, or ventricle
  • myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Code Also

Additional codes that may be required to fully describe the encounter.

  • the presence of hypertension (I10-I1A)

Source: inherited from I20-I25

Use Additional Code

Supplementary codes the tabular list directs you to add.

  • Use additional code, if applicable, to identify:
  • exposure to environmental tobacco smoke (Z77.22)
  • history of tobacco dependence (Z87.891)
  • occupational exposure to environmental tobacco smoke (Z57.31)
  • status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
  • tobacco dependence (F17.-)
  • tobacco use (Z72.0)

Coder workflow for I21

MedCoder structured workflow — derived from this code’s own official record

Before you code I21

  1. I21 is not reportable as written. Select the more specific code beneath it that the documentation supports. Codes are reported to the highest level of specificity the classification provides (Guidelines I.B.2).

    ReviewI21.0, I21.1, I21.2, I21.3, I21.4, I21.9, I21.A, I21.B

    See the relationships section · Guide: How to choose an ICD-10-CM code →

Choose the right path

  1. Does the documentation support one of the more specific codes beneath I21?
    Yes → Select that code and continue the checks below on its own page.
    No → I21 cannot be reported as written; query for the specificity its subcategory needs.

    ReviewI21.0, I21.1, I21.2, I21.3, I21.4, I21.9, I21.A, I21.B

Consider I21. Then work the Use Additional Code note and review the Code Also note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Acuity
Acute or chronic as documented; when both are documented and separate codes exist, both are reported with the acute code first (Guidelines I.B.8).
The conditions the Use Additional Code note names
Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Official instructions as workflow

  • Excludes2 — not part of I21(3 notes)

    Coding workflow: The conditions named in this note are not included in I21. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareI25.2, I24.1, I22

    See the official tabular notes · Guidelines I.A.12.b

  • Use Additional Code — after identifying I21(7 notes)

    Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with I21 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

    ReviewZ77.22, Z87.891, Z57.31, Z92.82, F17, Z72.0

    See the official tabular notes · Guidelines I.A.13

  • Code Also — related condition(1 note)

    Coding workflow: Review the related condition when both are documented and the instruction applies. A Code Also note does not fix sequencing; the order follows the circumstances of the encounter.

    See the official tabular notes · Guidelines I.A.17

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: A condition the Use Additional Code note names is documented.

Coding question: Is a second code reported with I21?

Path: Review the Use Additional Code note and the code it names.

Reason: The additional code is reported when the record documents the condition; a conditional instruction applies only when its condition is met (Guidelines I.A.13).

ReviewZ77.22, Z87.891, Z57.31, Z92.82, F17, Z72.0

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Acute myocardial infarction is a non-billable ICD-10-CM category code (I21). A more specific billable subcode must be selected for claims submission.

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 9: Diseases of the Circulatory System (I00 -I99)

For encounters occurring while the myocardial infarction is equal to, or less than, four weeks old, including transfers to another acute setting or a postacute setting, and the myocardial infarction meets the definition for “other diagnoses” (see Section III, Reporting Additional Diagnoses), codes from category I21 may continue to be reported. For encounters after the 4-week time frame and the patient is still receiving care related to the myocardial infarction, the appropriate aftercare code should be assigned, rather than a code from category I21. For old or healed myocardial infarctions not requiring further care, code I25.2, Old myocardial infarction, may be assigned.

Chapter 9: Diseases of the Circulatory System (I00 -I99)

4) Subsequent acute myocardial infarction A code from category I22, Subsequent ST elevation (STEMI) and non- ST elevation (NSTEMI) myocardial infarction, is to be used when a patient who has suffered a type 1 or unspecified AMI has a new AMI within the 4 week time frame of the initial AMI. A code from category I22 must be used in conjunction with a code from category I21. The sequencing of the I22 and I21 codes depends on the circumstances of the encounter.

Chapter 9: Diseases of the Circulatory System (I00 -I99)

If a subsequent myocardial infarction of one type occurs within 4 weeks of a myocardial infarction of a different type, assign the appropriate codes from category I21 to identify each type. Do not assign a code from I22. Codes from category I22 should only be assigned if both the initial and subsequent myocardial infarctions are type 1 or unspecified.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

  1. 7 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
  2. 1 Code Also note — a second code may apply; the guidelines leave its sequencing to the circumstances of the encounter. See the Code Also notes
  3. 3 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name I21 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 2 Excludes1 notes: I25.82 — Chronic total occlusion of coronary artery, I5A — Non-ischemic myocardial injury (non-traumatic).

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

Referenced by 2 Excludes2 notes: I74 — Arterial embolism and thrombosis, I82 — Other venous embolism and thrombosis.

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Referenced by 1 Code First instruction: Z92.82 — Status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility.

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

Referenced by 1 Code Also instruction: I16.1 — Hypertensive emergency.

These codes suggest coding this condition alongside when both are present.

Contextual Map

Every relationship of I21 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run I21 with these 14 related codes in Claim Check

Hierarchy

Excludes2

Use Additional Code

Referenced by Excludes1 notes

Referenced by Excludes2 notes

Referenced by Code First instructions

Referenced by Code Also instructions

Nearest codes (17)

Change history (3)

Common coding questions

Can I21 be billed directly?

No. I21 (Acute myocardial infarction) is a non-billable ICD-10-CM category code. A more specific billable subcode must be selected based on clinical documentation.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "I21 — Acute myocardial infarction." ICD-10-CM FY2026. https://medcoder.ai/icd10/code/i21-acute-myocardial-infarction

Change history

  • FY2018 — October 1, 2017
    Description revised
    ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction → Acute myocardial infarction
    FY2018 changes
  • FY2018 — October 1, 2017
    Short description revised
    STEMI & NSTEMI mocard infrc → Acute myocardial infarction
    FY2018 changes
  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction

Nearest Codes in This Family

Official ICD-10-CM classifications closest to I21 in its code family, with their registry titles.