I51.4 Myocarditis, unspecified

The ICD-10-CM code for Myocarditis, unspecified is I51.4 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

9: Diseases of the circulatory system (I00-I99)

Section

I30-I5A: Other forms of heart disease (I30-I5A)

Category I51

12 codes (10 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to I51.4:

• Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile)
• Acardiotrophia
• Arteriosclerosis, arteriosclerotic (diffuse) (obliterans) (of) (senile) (with calcification) › myocarditis

Inclusion Terms

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

U.S. Hospital Utilization

• An estimated 7,900 U.S. inpatient stays in 2023 included I51.4 among the documented diagnoses.
• 2,340 stays listed it as the principal diagnosis.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

I11 + addl code for I50/I51 heart conditions (incl I50.-, I51.4, I51.89, I51.9)

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.

Code separately if documented unrelated; assign I10 or I15; sequence per encounter

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.

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)