2026 ICD-10-CM Diagnosis Code I21.BMyocardial infarction with coronary microvascular dysfunction

ICD-10-CM Codes›I00–I99›I20-I25›I21

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

I21.B is a billable ICD-10-CM diagnosis code for myocardial infarction with coronary microvascular dysfunction. 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.

Code Identity

ICD-10-CM Code
I21.B
Billable Status
Yes — Valid for Submission
Code Describes
Myocardial infarction with coronary microvascular dysfunction
Short Description
Myocardial infarction with coronary microvascular dysfnct
Parent Code
I21
Acute myocardial infarction

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI20-I25Ischemic heart diseases
CategoryI21Acute myocardial infarction
This CodeI21.BMyocardial infarction with coronary microvascular dysfunction

Tabular List NotesGuidance

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

Inclusion Terms

  • Myocardial infarction with coronary microvascular disease
  • Myocardial infarction with nonobstructive coronary arteries MINOCA with microvascular disease

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.

    • Disease, diseased
      • coronary (artery)
        • microvascular
          • with
            • myocardial infarction
    • Dysfunction
      • coronary microvascular
        • with
          • myocardial infarction
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • with
          • coronary microvascular disease
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • with
          • coronary microvascular dysfunction
    • Infarct, infarction
      • myocardium, myocardial (acute) (with stated duration of 4 weeks or less)
        • with
          • nonobstructive coronary arteries [MINOCA] with microvascular disease

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

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.

Code History & ChangesHistory

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

  • I21.A9 - Other myocardial infarction type
FY 2024AddedAdded to the ICD-10-CM code setEffective October 1, 2023.
FY 2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About I21.BOverview

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

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

What MS-DRG does I21.B group to?

When myocardial infarction with coronary microvascular dysfunction 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.

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.