2026 ICD-10-CM Diagnosis Code I21.A1Myocardial infarction type 2

ICD-10-CM Codes›I00–I99›I20-I25›I21

ICD-10-CM I21.A1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I21.A1 is a billable ICD-10-CM diagnosis code for myocardial infarction type 2. 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. Coders also document this condition as myocardial infarction due to demand ischemia. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acute myocardial infarction.

Code Identity

ICD-10-CM Code
I21.A1
Billable Status
Yes — Valid for Submission
Code Describes
Myocardial infarction type 2
Short Description
Myocardial infarction type 2
Same as the full description in the CMS dataset.
Parent Code
I21.A
Other type of myocardial infarction

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI20-I25Ischemic heart diseases
CategoryI21Acute myocardial infarction
This CodeI21.A1Myocardial infarction type 2

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Myocardial infarction due to demand ischemia

Tabular List NotesGuidance

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

Inclusion Terms

  • Myocardial infarction due to demand ischemia
  • Myocardial infarction secondary to ischemic imbalance

Code First

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)
        • due to
          • demand ischemia
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • due to
          • ischemic imbalance
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • secondary to
          • demand ischemia
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • secondary to
          • ischemic imbalance
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • subsequent (recurrent) (reinfarction)
          • type 2
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • type 2
    • Ischemia, ischemic
      • demand (coronary)
        • with myocardial infarction
    • Ischemia, ischemic
      • demand (coronary)
        • resulting in myocardial infarction

Clinical ClassificationClinical

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

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

Patient EducationClinical

Heart Attack

Each year almost 800,000 Americans have a heart attack. A heart attack happens when blood flow to the heart suddenly becomes blocked. Without the blood coming in, the heart can't get oxygen. If not treated quickly, the heart muscle begins to die.

Read the full article at MedlinePlus

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

Convert I21.A1 to ICD-9-CMHistory

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

ICD-9-CM
410.90 AMI NOS, unspecified
Approximate The match is approximate rather than exact.
ICD-9-CM
410.91 AMI NOS, initial
Approximate The match is approximate rather than exact.
ICD-9-CM
410.92 AMI NOS, subsequent
Approximate The match is approximate rather than exact.

Code History & ChangesHistory

Replacement I21.A1 replaces the following previously assigned code(s):

  • I21.3 - ST elevation (STEMI) myocardial infarction of unsp site
FY 2018AddedAdded to the ICD-10-CM code setEffective October 1, 2017.
FY 2019–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About I21.A1Overview

Is I21.A1 (Other type of myocardial infarction) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report myocardial infarction type 2 on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does I21.A1 group to?

When myocardial infarction type 2 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.A1?

Under the General Equivalence Mappings, myocardial infarction type 2 converts to ICD-9-CM 410.90 (AMI NOS, unspecified), 410.91 (AMI NOS, initial), and 410.92 (AMI NOS, subsequent). 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.