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I51.4 ICD-10-CM Code: Myocarditis, unspecified

Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.

Coding at a Glance

Tabular directives
3 inclusion terms · 1 Excludes1 · 1 Excludes2
Risk adjustment
CMS-HCC V28: 1 category · CMS-HCC V22 category 85 · RxHCC V08 category 186

Inpatient Payment Groups (MS-DRG)

Potential MS-DRG participation — not a DRG assignment.

MS-DRGs this diagnosis helps define, as principal or secondary, per the CMS ICD-10-CM/PCS MS-DRG Definitions Manual v43, Appendix B.

  • MS-DRG 314 — OTHER CIRCULATORY SYSTEM DIAGNOSES WITH MCC (MDC 05)
  • MS-DRG 315 — OTHER CIRCULATORY SYSTEM DIAGNOSES WITH CC (MDC 05)
  • MS-DRG 316 — OTHER CIRCULATORY SYSTEM DIAGNOSES WITHOUT CC/MCC (MDC 05)

A diagnosis appearing in a group's logic does not by itself determine the DRG assigned to a stay; the grouper uses the full claim.

Risk Adjustment (CMS-HCC)

Payment categories this diagnosis maps to under CMS-HCC V28, payment year 2026.

  • HCC 227 — Cardiomyopathy/Myocarditis

Other models: CMS-HCC V22 HCC 85 · RxHCC V08 HCC 186

Risk scores depend on the enrollee's full accepted diagnosis set and segment; a category mapping alone does not determine payment.

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for I51.4 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on I51.4 itself; “inherited from” names the category or block whose note applies here.

Inclusion Terms

Alternative terms the tabular list files under this code.

  • Chronic (interstitial) myocarditis
  • Myocardial fibrosis
  • Myocarditis NOS

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Source: inherited from I51

Coder workflow for I51.4

MedCoder structured workflow — derived from this code’s own official record

Before you code I51.4

  1. Unspecified does not mean incorrect. When the record gives no greater specificity, I51.4 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

    ReviewI51.0, I51.1, I51.2, I51.3, I51.5, I51.7, I51.8

    See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

  2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with I51.4. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the record document the detail a more specific sibling code needs?
    Yes → Review the specific siblings in this subcategory.
    No → Continue — I51.4 is appropriate when the documentation goes no further.

    ReviewI51.0, I51.1, I51.2, I51.3, I51.5, I51.7, I51.8

  2. Does the documentation support a condition named in I51.4’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewI40

Consider I51.4. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Any detail beyond this code’s title
What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

  • Excludes1 — check before selecting I51.4(1 note)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with I51.4: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareI40

    See the official tabular notes · Guidelines I.A.12.a

  • Excludes2 — not part of I51.4(1 note)

    Coding workflow: The conditions named in this note are not included in I51.4. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: The provider documents the condition in the terms of this code’s title and records no further detail.

Coding question: Is a more specific sibling code supportable?

Path: Review the specific siblings in this subcategory and what each requires the record to state.

Reason: A more specific code needs documentation of the distinguishing element; without it the unspecified code is appropriate, and a provider query is the route to specificity (Guidelines I.A.9.b, I.B.18).

ReviewI51.0, I51.1, I51.2, I51.3, I51.5, I51.7, I51.8

Documentation: Both the condition I51.4 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewI40

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Code Overview

Myocarditis, unspecified is a billable ICD-10-CM diagnosis code (I51.4).

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Indexed Clinical Terms (3)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

Official Coding Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Official source data — quoted verbatim from the CMS/NCHS Official Guidelines

Verbatim excerpts from the ICD-10-CM Official Guidelines for Coding and Reporting (CMS/NCHS) that govern this code.

Chapter 9: Diseases of the Circulatory System (I00 -I99)

1) Hypertension with Heart Disease Hypertension with heart conditions classified to I50.-, Heart failure, I51.4, Myocarditis, unspecified, I51.89, Other ill-defined heart diseases, and I51.9, Heart disease, unspecified, is assigned to a code from category I11, Hypertensive heart disease. Use additional code(s) from category I50, Heart failure, or I51, Complications and ill-defined descriptions of heart disease, to identify the heart condition.

Chapter 9: Diseases of the Circulatory System (I00 -I99)

The same heart conditions (I50.-, I51.4-I51.7, I51.89, I51.9) with hypertension are coded separately if the provider has documented they are unrelated to the hypertension. The applicable hypertension code I10, Essential (primary) hypertension, or a code from category I15, Secondary hypertension, should be assigned. Sequence according to the circumstances of the admission/encounter.

Verify Before Coding

  • No Medicare Code Editor or MS-DRG Definitions Manual restrictions apply to this code.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name I51.4 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Excludes1 note: I09.0 — Rheumatic myocarditis.

These codes’ tabular lists mark this diagnosis as mutually exclusive — not reported together unless the conditions are documented as unrelated.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: not on the CMS CC/MCC list — as a secondary diagnosis this code does not change MS-DRG severity for that release.

Named in the grouper logic of 3 MS-DRGs: DRG 314 (MDC 05), DRG 315 (MDC 05), DRG 316 (MDC 05).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):CIR005 — Myocarditis and cardiomyopathy (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Cardiomyopathy/Myocarditis) for risk-adjusted payment.

A36.81 — Diphtheritic cardiomyopathy, B33.24 — Viral cardiomyopathy, I42.0 — Dilated cardiomyopathy, I42.1 — Obstructive hypertrophic cardiomyopathy, I42.2 — Other hypertrophic cardiomyopathy, I42.3 — Endomyocardial (eosinophilic) disease, I42.4 — Endocardial fibroelastosis, I42.5 — Other restrictive cardiomyopathy, I42.6 — Alcoholic cardiomyopathy, I42.8 — Other cardiomyopathies, I42.9 — Cardiomyopathy, unspecified, I43 — Cardiomyopathy in diseases classified elsewhere, I51.5 — Myocardial degeneration

Related risk categories

These categories interact through CMS's HCC hierarchy — one can suppress the other's risk-adjustment weight when both are present on a claim.

Heart Failure with Heart Assist Device/Artificial Heart, Acute on Chronic Heart Failure, Acute Heart Failure (Excludes Acute on Chronic), Heart Failure, Except End-Stage and Acute

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Myocarditis and cardiomyopathy).

I25.5 — Ischemic cardiomyopathy, I40.0 — Infective myocarditis, I40.1 — Isolated myocarditis, I40.8 — Other acute myocarditis, I40.9 — Acute myocarditis, unspecified, I41 — Myocarditis in diseases classified elsewhere, I42.0 — Dilated cardiomyopathy, I42.1 — Obstructive hypertrophic cardiomyopathy, I42.2 — Other hypertrophic cardiomyopathy, I42.3 — Endomyocardial (eosinophilic) disease, I42.4 — Endocardial fibroelastosis, I42.5 — Other restrictive cardiomyopathy, I42.6 — Alcoholic cardiomyopathy, I42.7 — Cardiomyopathy due to drug and external agent, I42.8 — Other cardiomyopathies, I42.9 — Cardiomyopathy, unspecified, I43 — Cardiomyopathy in diseases classified elsewhere, J10.82 — Influenza due to other identified influenza virus with myocarditis, J11.82 — Influenza due to unidentified influenza virus with myocarditis, O90.3 — Peripartum cardiomyopathy, +12 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Arteriosclerosis, arteriosclerotic”, “Myocarditis”; these codes share that main term but sit in a different category of the Tabular List.

I25.810 — Atherosclerosis of coronary artery bypass graft(s) without angina pectoris (coronary, bypass graft), I25.811 — Atherosclerosis of native coronary artery of transplanted heart without angina pectoris (coronary, transplanted heart), I25.812 — Atherosclerosis of bypass graft of coronary artery of transplanted heart without angina pectoris (coronary, transplanted heart, bypass graft), I25.83 — Coronary atherosclerosis due to lipid rich plaque (coronary, due to, lipid rich plaque), I25.84 — Coronary atherosclerosis due to calcified coronary lesion (coronary, due to, calcified coronary lesion), I27.0 — Primary pulmonary hypertension (pulmonary), I40.0 — Infective myocarditis (septic), I40.1 — Isolated myocarditis (isolated), I40.8 — Other acute myocarditis (toxic), I40.9 — Acute myocarditis, unspecified (active), I65.2 — Occlusion and stenosis of carotid artery (carotid), I67.2 — Cerebral atherosclerosis (brain), I70.0 — Atherosclerosis of aorta (aorta), I70.1 — Atherosclerosis of renal artery (renal, artery), I70.201 — Unspecified atherosclerosis of native arteries of extremities, right leg (extremities, leg, right), I70.202 — Unspecified atherosclerosis of native arteries of extremities, left leg (extremities, leg, left), I70.203 — Unspecified atherosclerosis of native arteries of extremities, bilateral legs (extremities, leg, bilateral), I70.208 — Unspecified atherosclerosis of native arteries of extremities, other extremity (extremities, specified site NEC), I70.209 — Unspecified atherosclerosis of native arteries of extremities, unspecified extremity (extremities), I70.211 — Atherosclerosis of native arteries of extremities with intermittent claudication, right leg (extremities, leg, right, with, intermittent claudication), +297 more

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Prothrombin Time Test and INR (PT/INR)

Contextual Map

Every relationship of I51.4 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run I51.4 with these 2 related codes in Claim Check

Hierarchy

Excludes1

  • I40 — Acute myocarditis[Excludes1]: “acute or subacute myocarditis (I40.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Referenced by Excludes1 notes

  • I09.0 — Rheumatic myocarditis[Excludes1]: “myocarditis not specified as rheumatic (I51.4)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

Risk adjustment (CMS-HCC)

  • HCC 227 — Cardiomyopathy/Myocarditis [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

MDC crossing

  • MDC 05 — Diseases and Disorders of the Circulatory System[MDC crossing]: “Diseases and Disorders of the Circulatory System — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 17,209 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

  • Acardiotrophia[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Arteriosclerosis, arteriosclerotic (diffuse) (obliterans) (of) (senile) (with calcification), myocarditis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
  • Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (11)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page
Coding guidelines Official source data
ICD-10-CM Official Guidelines for Coding and Reporting (FY2026), quoted by section Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page
Inpatient payment groups Official source data
CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page
Risk adjustment Official source data
2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Myocarditis, unspecified

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027 (effective October 1, 2026), and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to I51.4 in its code family, with their registry titles.

View all codes in the I51 family