ICD-10-CM 2027 diagnosis code
I40.1Isolated myocarditis
I40.1 is a valid, billable ICD-10-CM code for isolated myocarditis. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.
Looking up by condition? See ICD-10 code for Abramov-Fiedler myocarditis.
Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About I40.1
I40.1 is the ICD-10-CM diagnosis code for isolated myocarditis. It belongs to category I40 (acute myocarditis), block I30-I5A (other forms of heart disease) and chapter 9 (diseases of the circulatory system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within I40 (acute myocarditis), I40.1 is specifically for isolated myocarditis. Related codes cover infective myocarditis (I40.0), other acute myocarditis (I40.8) and unspecified (I40.9).
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 314 (Other Circulatory System Diagnoses with MCC, relative weight 2.0873), DRG 315 (Other Circulatory System Diagnoses with CC, relative weight 0.9508), DRG 316 (Other Circulatory System Diagnoses without CC/MCC, relative weight 0.6677), DRG 974 (HIV with Major Related Condition with MCC, relative weight 3.0506), DRG 975 (HIV with Major Related Condition with CC, relative weight 1.3252) and DRG 976 (HIV with Major Related Condition without CC/MCC, relative weight 0.8124), in MDC 05 (Diseases and Disorders of the Circulatory System) and MDC 25 (Human Immunodeficiency Virus Infections), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Before ICD-10, this condition was coded in ICD-9-CM as 422.91 (idiopathic myocarditis).
Coding notes
- Fiedler's myocarditis
- Giant cell myocarditis
- Idiopathic myocarditis
Notes that apply from higher levels
Instructions written at a parent level also apply to I40.1.
› From I40 Acute myocarditis
- subacute myocarditis
- acute rheumatic myocarditis (I01.2)
Broader instructions also apply from Chapter 9: Diseases of the circulatory system.
Alphabetic index entries
10 entriesTerms in the official ICD-10-CM index that lead to I40.1.
- Abramov-Fiedler myocarditis (acute isolated myocarditis)
- Fiedler's › myocarditis (acute)
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › acute or subacute (interstitial) › idiopathic
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › eosinophilic
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › Fiedler's (acute) (isolated)
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › giant cell (acute) (subacute)
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › granulomatous (idiopathic) (isolated) (nonspecific)
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › idiopathic (granulomatous)
- Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › isolated (acute)
- Syndrome › Fiedler's
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 05 · Diseases and Disorders of the Circulatory System
MDC 25 · Human Immunodeficiency Virus Infections
ICD-9-CM equivalent
Converter →- 422.91Idiopathic myocarditisapproximate
From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about I40.1
Is I40.1 billable?
- Yes. I40.1 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can I40.1 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict I40.1 as a principal diagnosis.
Is I40.1 a CC or MCC?
- I40.1 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.
What DRG does I40.1 group to?
- I40.1 is used in the MS-DRG v44.0 logic for MS-DRG 314 (Other Circulatory System Diagnoses with MCC), MS-DRG 315 (Other Circulatory System Diagnoses with CC), MS-DRG 316 (Other Circulatory System Diagnoses without CC/MCC), MS-DRG 974 (HIV with Major Related Condition with MCC), MS-DRG 975 (HIV with Major Related Condition with CC) and MS-DRG 976 (HIV with Major Related Condition without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.
What is the ICD-9 code for I40.1?
- The CMS General Equivalence Mappings map I40.1 to ICD-9-CM 422.91.