ICD-10 Code I40.8 – Other acute myocarditis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I40.8 – Other acute myocarditis
What it is
I40.8 identifies acute inflammation of the heart muscle that does not fit the more specific myocarditis categories. Use it when the provider documents another acute myocarditis type and the record supports an acute inflammatory process.
Clinical signs
Clinical features vary; refer to documentation. Common findings may include chest pain, shortness of breath, arrhythmia, or evidence of myocardial inflammation on evaluation.
When to use this code
Use this code when the clinician clearly documents other acute myocarditis and no more specific ICD-10-CM myocarditis code applies. It may also fit cases where the diagnosis is acute myocarditis but the cause or subtype is not further specified. Check documentation for acuity and specificity before assigning I40.8.
Do not use for
Do not use I40.8 for chronic myocarditis, myocarditis with a more specific code, or noninflammatory cardiac conditions. If the record does not confirm acute myocarditis, check documentation.
Coding tip
Assign I40.8 only when the provider’s wording supports an acute myocarditis diagnosis and no better-defined code is available.