2026 ICD-10-CM Diagnosis Code I42.4Endocardial fibroelastosis
ICD-10-CM Codes›I00–I99›I30-I5A›I42
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 227
- Chronic Condition
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. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 112 closely related codes. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Myocarditis and cardiomyopathy.
For Medicare Advantage risk adjustment, I42.4 maps to CMS-HCC Category 227 (Cardiomyopathy/Myocarditis) under the V28 model, adding a risk factor of about 0.189 for a community, non-dual, aged beneficiary in payment year 2026.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
I42.4 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
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
These terms are the conditions for which that code is to be used. The terms may be synonyms of the code title, or, in the case of "other specified" codes, the terms are a list of the various conditions assigned to that code. The inclusion terms are not necessarily exhaustive. Additional terms found only in the Alphabetic Index may also be assigned to a code.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Elastomyofibrosis I42.4
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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
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Convert I42.4 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About I42.4Overview
What is the ICD-10 code for endocardial fibroelastosis?
The ICD-10-CM code for endocardial fibroelastosis is I42.4 (sometimes written as I424). It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
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.
Is I42.4 a CC or MCC?
CMS lists I42.4 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 112 closely related codes in its exclusion list.
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.
What HCC is I42.4?
I42.4 (endocardial fibroelastosis) maps to CMS-HCC Category 227 (Cardiomyopathy/Myocarditis), commonly written as HCC 227, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 85 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 186.
Does I42.4 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, I42.4 adds a risk adjustment factor of about 0.189 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.145 to 0.200 depending on the payment segment). A more severe related category (HCC 221, HCC 222, HCC 223, HCC 224, HCC 225, and HCC 226) supersedes it when both are reported. See the full factor table on the HCC 227 category page.
