I40.9 Acute myocarditis, unspecified

Billable ICD-10-CM code, FY2026. Acts as a Major Complication or Comorbidity (MCC) as a secondary diagnosis.

Applies from I40 Acute myocarditis

Includes

• subacute myocarditis

Excludes1 (never code together)

• acute rheumatic myocarditis (I01.2)

MS-DRG index

Defines the logic of DRG(s) 314-316 in MDC 05.

Approximate ICD-9-CM (GEMs)

• 422.90 Acute myocarditis, unspecified

Code annotations containing back-references to I40.9

Back-references to I40

• Type 1 Excludes: I51.4 Myocarditis, unspecified ("acute or subacute myocarditis (I40.-)")
• Code First: I5A Non-ischemic myocardial injury (non-traumatic) ("acute myocarditis (I40.-)")
• Code Also: M35.81 Multisystem inflammatory syndrome ("acute myocarditis (I40.-)")

Diagnosis Index entries for I40.9

• Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › active
• Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › acute or subacute (interstitial)
• Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › nonrheumatic, active
• Myocarditis (with arteriosclerosis)(chronic)(fibroid) (interstitial) (old) (progressive) (senile) › parenchymatous
• Rupture, ruptured › cardiac (auricle) (ventricle) (wall) › infectional

Nearby codes

• I40 Acute myocarditis
• I40.0 Infective myocarditis
• I40.1 Isolated myocarditis
• I40.8 Other acute myocarditis
• I40.9 Acute myocarditis, unspecified (this code)