ICD-10 Code I40 – Acute myocarditis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I40 – Acute myocarditis
What it is
I40 identifies acute inflammation of the myocardium, the heart muscle. Use it when documentation describes a sudden or recent myocarditis diagnosis.
Clinical signs
Clinical features vary; refer to documentation. Commonly noted findings include chest pain, dyspnea, palpitations, arrhythmias, or heart failure symptoms, with supportive cardiac testing when documented.
When to use this code
Use I40 when the provider clearly documents acute myocarditis, including infectious or other acute inflammatory heart muscle involvement. Code the condition based on the documented diagnosis, not on nonspecific chest symptoms alone. If the record does not specify myocarditis, check documentation.
Do not use for
Do not use I40 for chronic myocarditis, isolated pericarditis, or nonspecific cardiomyopathy without myocarditis documentation. If the chart is unclear, check documentation.
Coding tip
Confirm that the provider states “acute myocarditis” or equivalent wording before assigning I40.