I51.9 ICD-10-CM Code: Heart disease, unspecified

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for I51.9 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 I51.9 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for I51.9

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

Before you code I51.9

1. Unspecified does not mean incorrect. When the record gives no greater specificity, I51.9 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) →

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 — I51.9 is appropriate when the documentation goes no further.

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

Consider I51.9. 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

• Excludes2 — not part of I51.9(1 note)

  Coding workflow: The conditions named in this note are not included in I51.9. 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

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.

Indexed Clinical Terms (7)

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.

• Cardiopathy
• Complication (s) (from) (of), heart
• Disease, diseased, heart (organic)
• Disease, diseased, heart (organic), cryptogenic
• Dysfunction, ventricular
• Lesion (s) (nontraumatic), cardiac
• Morbus, cordis

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.

Don’t confuse I51.9 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of I51.9 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• I00— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of heart disease specified as rheumatic adds I00; it is not part of this code and both may be reported when both are documented.

  Full comparison: I51.9 vs I00 →

• I09— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of heart disease specified as rheumatic adds I09; it is not part of this code and both may be reported when both are documented.

  Full comparison: I51.9 vs I09 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

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

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 2 MS-DRGs: DRG 302 (MDC 05), DRG 303 (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):CIR015 — Other and ill-defined heart disease (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 clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Other and ill-defined heart disease).

I25.3 — Aneurysm of heart, I25.41 — Coronary artery aneurysm, I51.0 — Cardiac septal defect, acquired, I51.1 — Rupture of chordae tendineae, not elsewhere classified, I51.2 — Rupture of papillary muscle, not elsewhere classified, I51.3 — Intracardiac thrombosis, not elsewhere classified, I51.5 — Myocardial degeneration, I51.7 — Cardiomegaly, I51.81 — Takotsubo syndrome, I51.89 — Other ill-defined heart diseases, I52 — Other heart disorders in diseases classified elsewhere, I5A — Non-ischemic myocardial injury (non-traumatic), M05.30 — Rheumatoid heart disease with rheumatoid arthritis of unspecified site, M05.311 — Rheumatoid heart disease with rheumatoid arthritis of right shoulder, M05.312 — Rheumatoid heart disease with rheumatoid arthritis of left shoulder, M05.319 — Rheumatoid heart disease with rheumatoid arthritis of unspecified shoulder, M05.321 — Rheumatoid heart disease with rheumatoid arthritis of right elbow, M05.322 — Rheumatoid heart disease with rheumatoid arthritis of left elbow, M05.329 — Rheumatoid heart disease with rheumatoid arthritis of unspecified elbow, M05.331 — Rheumatoid heart disease with rheumatoid arthritis of right wrist, +15 more

Same Index main term, other category

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

I21.B — Myocardial infarction with coronary microvascular dysfunction (coronary microvascular, with, myocardial infarction), I24.81 — Acute coronary microvascular dysfunction (coronary microvascular, acute), I25.85 — Chronic coronary microvascular dysfunction (coronary microvascular), I27.841 — Fontan-associated lymphatic dysfunction (lymphatic, Fontan-associated), I35.9 — Nonrheumatic aortic valve disorder, unspecified (aortic), I36.9 — Nonrheumatic tricuspid valve disorder, unspecified (tricuspid, nonrheumatic), I37.9 — Nonrheumatic pulmonary valve disorder, unspecified (pulmonary, valve), I42.9 — Cardiomyopathy, unspecified (idiopathic), I49.5 — Sick sinus syndrome (sinoatrial node), I50.9 — Heart failure, unspecified (ventricular, with congestive heart failure), I67.4 — Hypertensive encephalopathy (cerebrovascular, hypertensive), I67.9 — Cerebrovascular disease, unspecified (cerebrovascular), I99.9 — Unspecified disorder of circulatory system (vascular), J32.0 — Chronic maxillary sinusitis (maxillary sinus), J34.89 — Other specified disorders of nose and nasal sinuses (nose), J35.9 — Chronic disease of tonsils and adenoids, unspecified (tonsillar fossa), J39.2 — Other diseases of pharynx (pharynx), J4A.0 — Restrictive allograft syndrome (chronic, lung allograft, mixed), J4A.8 — Other chronic lung allograft dysfunction (chronic, lung allograft, specified NEC), J4A.9 — Chronic lung allograft dysfunction, unspecified (chronic, lung allograft), +217 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.

Lipid Panel

Contextual Map

Every relationship of I51.9 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.

Hierarchy

• I00-I99 — Chapter 9: Diseases of the Circulatory System (I00-I99) (I00-I99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I30-I5A — Other forms of heart disease[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Clinical classification (CCSR)

• CIR015 — Other and ill-defined heart disease[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

MS-DRG Grouper

• DRG 302 — ATHEROSCLEROSIS WITH MCC[MS-DRG]: “ATHEROSCLEROSIS WITH MCC (MDC 05)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 303 — ATHEROSCLEROSIS WITHOUT MCC[MS-DRG]: “ATHEROSCLEROSIS WITHOUT MCC (MDC 05)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

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

• Cardiopathy[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Complication (s) (from) (of), heart[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Disease, diseased, heart (organic)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Disease, diseased, heart (organic), cryptogenic[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Dysfunction, ventricular[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Lesion (s) (nontraumatic), cardiac[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026
• Morbus, cordis[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (11)

• I51 — Complications and ill-defined descriptions of heart disease[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.0 — Cardiac septal defect, acquired[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.1 — Rupture of chordae tendineae, not elsewhere classified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.2 — Rupture of papillary muscle, not elsewhere classified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.3 — Intracardiac thrombosis, not elsewhere classified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.4 — Myocarditis, unspecified[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.5 — Myocardial degeneration[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• I51.7 — Cardiomegaly[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 3 more

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

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

Nearest Codes in This Family

Official ICD-10-CM classifications closest to I51.9 in its code family, with their registry titles.

• I51.0 — Cardiac septal defect, acquired
• I51.1 — Rupture of chordae tendineae, not elsewhere classified
• I51.2 — Rupture of papillary muscle, not elsewhere classified
• I51.3 — Intracardiac thrombosis, not elsewhere classified
• I51.4 — Myocarditis, unspecified
• I51.5 — Myocardial degeneration
• I51.7 — Cardiomegaly
• I51.8 — Other ill-defined heart diseases
• I51.81 — Takotsubo syndrome
• I51.89 — Other ill-defined heart diseases

View all codes in the I51 family