ICD-10 I40.1
Billable / Specific MCCIsolated myocarditis
About ICD-10-CM I40.1
ICD-10-CM code I40.1 represents Isolated myocarditis. This is a billable/specific code in the Circulatory System chapter (block I40). The 2026 edition of ICD-10-CM I40.1 became effective on October 1, 2025.
Coding Tips for I40.1
Specialist guidance from the PayerReady Medical Coding Team. Specificity warnings, HCC capture rules, sequencing notes.
I40.1 is designated MCC for MS-DRG grouping. On inpatient claims, this code can shift the DRG to the with-MCC variant when documented as a present-on-admission secondary diagnosis. Hospital CDI programs flag MCC opportunities during chart review. Failure to capture this code may leave 30 to 80 percent of the inpatient stay revenue unrealized.
Inclusion Terms / Approximate Synonyms
Clinical terms and conditions classified under I40.1. Per CMS ICD-10-CM Tabular 2026.
- Fiedler's myocarditis
- Giant cell myocarditis
- Idiopathic myocarditis
Inpatient DRG Impact, MCC
codes Isolated myocarditis. As a Major Complication/Comorbidity (MCC), this can shift the DRG assignment to a higher-weighted category, substantial reimbursement impact.
Medicare LCD Coverage for I40.1
Local Coverage Determinations (LCDs) from CMS MACs that list I40.1 as a covered diagnosis.
Showing top 10 of 269 total . Click a CPT for full coverage scope.
Commercial Payer Coverage
Coverage policies from major commercial payers referencing I40.1.
5 Medicare
1 Aetna
CPT Codes Commonly Billed with I40.1
Procedures frequently paired with this diagnosis based on PayerReady's Dx↔Px linkage data.
We don't have CPT pairings indexed for this specific code yet. Use the CPT search above to find common procedures, or check your payer's published medical policy for code-specific guidance.
Convert I40.1 to ICD-9-CM
Per CMS General Equivalence Mappings (GEMs), useful for legacy data review and historical claim analysis.
| ICD-10 | ICD-9 | Mapping Flags |
|---|---|---|
| I40.1 | 42291 | 10000 |
Flags format (5 digits): Approximate · No Map · Combination · Scenario · Choice List. Source: CMS 2017 GEMs (final version).
Codes Adjacent To I40.1
Other codes in section I30-I5A (Other forms of heart disease).
ICD-10 I40.1, Billing FAQ
Is ICD-10 code I40.1 billable? +
Yes, I40.1 is a billable ICD-10-CM code that can appear as a primary or secondary diagnosis on claims.
What other names or terms map to I40.1? +
ICD-10 I40.1 includes: Fiedler's myocarditis; Giant cell myocarditis; Idiopathic myocarditis.
Is I40.1 a CC or MCC for inpatient DRG? +
Yes, this code is designated as MCC. Documenting as a secondary diagnosis on inpatient claims can shift the DRG to a higher-weighted category.
What ICD-9 codes does I40.1 map to? +
Per CMS GEMs, I40.1 maps to ICD-9 codes: 42291. Useful for legacy data review and historical claim analysis.
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Reviewed by the PayerReady Medical Coding Team
Verified against the CMS 2026 code set on May 31, 2026.
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