2026 ICD-10-CM Diagnosis Code I42.4Endocardial fibroelastosis

ICD-10-CM Codes›I00–I99›I30-I5A›I42

ICD-10-CM I42.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I42.4 is a billable ICD-10-CM diagnosis code for endocardial fibroelastosis. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myocarditis and cardiomyopathy.

Code Identity

ICD-10-CM Code
I42.4
Billable Status
Yes — Valid for Submission
Code Describes
Endocardial fibroelastosis
Short Description
Endocardial fibroelastosis
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 CodeI42.4Endocardial fibroelastosis

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Cardiomyopathy and renal anomaly syndrome
  • Congenital endocardial fibroelastosis
  • Endocardial fibroelastosis
  • Endocardial fibroelastosis of left atrium
  • Endocardial fibroelastosis of right atrium
  • Hydrocephalus with endocardial fibroelastosis and cataract syndrome
  • Primary endocardial fibroelastosis
  • Primary endocardial fibroelastosis of left ventricle
  • Primary endocardial fibroelastosis of right ventricle
  • Restrictive cardiomyopathy secondary to endocardial fibroelastosis
  • Secondary restrictive cardiomyopathy

Tabular List NotesGuidance

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

Inclusion Terms

  • Congenital cardiomyopathy
  • Elastomyofibrosis

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.

    • Anomaly, anomalous(congenital) (unspecified type)
      • heart
        • fibroelastosis cordis
    • Cardiomyopathy(familial) (idiopathic)
      • congenital
    • Cardiomyopathy(familial) (idiopathic)
      • newborn
        • congenital
    • Elastomyofibrosis
    • Fibroelastosis(cordis) (endocardial) (endomyocardial)
    • Newborn(infant) (liveborn) (singleton)
      • affected by
        • cardiomyopathy
          • congenital
    • Sclerosis, sclerotic
      • subendocardial, congenital

Clinical ClassificationClinical

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

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

Clinical InformationClinical

  • Endocardial Fibroelastosis

    a condition characterized by the thickening of endocardium due to proliferation of fibrous and elastic tissue, usually in the left ventricle leading to impaired cardiac function (cardiomyopathy, restrictive). it is most commonly seen in young children and rarely in adults. it is often associated with congenital heart anomalies (heart defects congenital;) infection; or gene mutation. defects in the tafazzin protein, encoded by taz gene, result in a form of autosomal dominant familial endocardial fibroelastosis.

  • Endocardial Fibroelastosis

    a rare disorder characterized by diffuse thickening of the endocardium. it presents with unexplained heart failure.

  • TAFAZZIN wt Allele|BTHS|Barth Syndrome Gene|CMD3A|Cardiomyopathy, Dilated 3A (X-Linked) Gene|EFE|EFE2|Endocardial Fibroelastosis 2 Gene|G4.5|LVNCX|TAZ|TAZ1|Tafazzin, Phospholipid-Lysophospholipid Transacylase wt Allele|Taz1

    human tafazzin wild-type allele is located in the vicinity of xq28 and is approximately 10 kb in length. this allele, which encodes tafazzin protein, plays a role in phospholipid metabolism, including cardiolipin remodeling. mutations in the gene are associated with barth syndrome, dilated cardiomyopathy (dcm), hypertrophic dcm, endocardial fibroelastosis and left ventricular noncompaction.

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 I42.4 to ICD-9-CMHistory

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

ICD-9-CM
425.3 Endocard fibroelastosis
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 I42.4Overview

Is I42.4 (Cardiomyopathy) a billable code?

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

What MS-DRG does I42.4 group to?

When endocardial fibroelastosis 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 I42.4?

Under the General Equivalence Mappings, endocardial fibroelastosis converts to ICD-9-CM 425.3 (endocard fibroelastosis). 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.