I40.1
Isolated myocarditis
I40.1 (also written I401) is a billable ICD-10-CM diagnosis code for isolated myocarditis. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 4 codes in category I40 (Acute myocarditis). The Alphabetic Index lists it under 10 entries. Its coding notes include 1 Excludes1 entry and 10 Excludes2 entries.
Excludes1
Not coded here. The listed conditions generally should not be reported together.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
Also from chapter/block level (10 notes)
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
- systemic connective tissue disorders (M30-M36)
- transient cerebral ischemic attacks and related syndromes (G45.-)
Care settings
How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.
Home Health Primary
Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the MMTA - Cardiac and Circulatory clinical group.
Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026Hospital MCC
Counts as a major complication or comorbidity (MCC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 22 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.
Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix CIncludes
Further defines or gives examples of the content of the category.
- subacute myocarditis
Inclusion terms
Conditions classified to this code.
- Fiedler's myocarditis
- Giant cell myocarditis
- Idiopathic myocarditis
Alphabetic Index terms
Terms the official Alphabetic Index lists for this code. 10 entries
- 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