2026 ICD-10-CM Diagnosis Code I42.1Obstructive hypertrophic cardiomyopathy

ICD-10-CM Codes›I00–I99›I30-I5A›I42

ICD-10-CM I42.1
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I42.1 is a billable ICD-10-CM diagnosis code for obstructive hypertrophic cardiomyopathy. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 314 through 316. Coders also document this condition as hypertrophic obstructive cardiomyopathy. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myocarditis and cardiomyopathy.

Code Identity

ICD-10-CM Code
I42.1
Billable Status
Yes — Valid for Submission
Code Describes
Obstructive hypertrophic cardiomyopathy
Short Description
Obstructive hypertrophic cardiomyopathy
Same as the full description in the CMS dataset.
Parent Code
I42
Cardiomyopathy

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI30-I5AOther forms of heart disease
CategoryI42Cardiomyopathy
This CodeI42.1Obstructive hypertrophic cardiomyopathy

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Hypertrophic obstructive cardiomyopathy

Tabular List NotesGuidance

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

Inclusion Terms

  • Hypertrophic subaortic stenosis (idiopathic)

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.

    • Cardiomyopathy(familial) (idiopathic)
      • hypertrophic (nonobstructive)
        • obstructive
    • Myocardiopathy(congestive) (constrictive) (familial) (hypertrophic nonobstructive) (idiopathic) (infiltrative) (obstructive) (primary) (restrictive) (sporadic)
      • hypertrophic obstructive
    • Stenosis, stenotic(cicatricial)
      • hypertrophic subaortic (idiopathic)
    • Stenosis, stenotic(cicatricial)
      • myocardium, myocardial
        • hypertrophic subaortic (idiopathic)
    • Stenosis, stenotic(cicatricial)
      • subaortic (congenital)
        • hypertrophic (idiopathic)
    • Stricture
      • myocardium, myocardial
        • hypertrophic subaortic (idiopathic)
    • Stricture
      • subaortic
        • hypertrophic (acquired) (idiopathic)

Clinical ClassificationClinical

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

CCSR CIR005
Myocarditis and cardiomyopathy
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Cardiomyopathy

Cardiomyopathy is the name for diseases of the heart muscle. These diseases enlarge your heart muscle or make it thicker and more rigid than normal. In rare cases, scar tissue replaces the muscle tissue.

Read the full article at MedlinePlus

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

Convert I42.1 to ICD-9-CMHistory

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

ICD-9-CM
425.11 Hyprtrophc obst cardiomy
Exact Match The mapping is direct, with no qualifiers.

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 I42.1Overview

Is I42.1 (Cardiomyopathy) a billable code?

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

What MS-DRG does I42.1 group to?

When obstructive hypertrophic cardiomyopathy is the principal diagnosis on an inpatient stay, it groups to MS-DRG 314, 315, 316, with relative weights from 0.6821 to 2.0852 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of I42.1?

Under the General Equivalence Mappings, obstructive hypertrophic cardiomyopathy converts to ICD-9-CM 425.11 (hyprtrophc obst cardiomy). The mapping is a direct match.

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.