ICD-10 Code I33.9 – Acute and subacute endocarditis, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I33.9 – Acute and subacute endocarditis, unspecified
What it is
I33.9 identifies acute or subacute endocarditis when the valve or site is not specified. It is used for an infection or inflammation of the heart lining or valves, with no documented organism or structure.
Clinical signs
Clinical features vary; refer to documentation. Commonly documented findings include fever, new or changed heart murmur, embolic phenomena, or evidence of valvular infection on imaging or cultures.
When to use this code
Use this code when the provider documents acute or subacute endocarditis but does not name the valve, organism, or other qualifying detail. It also fits cases where the record supports endocarditis, yet specificity is missing. Check documentation if the note suggests infective endocarditis with a more precise code available.
Do not use for
Do not use I33.9 if the provider documents a specific valve, organism, or a different type of endocarditis. Do not assign it for noninfective cardiac conditions or when the diagnosis is only suspected.
Coding tip
Query for the affected valve, organism, and acuity when the chart says endocarditis, because more specific coding may be possible.