ICD-10 Code I33 – Acute and subacute endocarditis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I33 – Acute and subacute endocarditis
What it is
I33 identifies acute or subacute inflammation of the endocardium, usually involving the heart valves. Use it when documentation states endocarditis and does not specify an organism or a more specific category.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings include fever, new or changing heart murmur, embolic phenomena, and evidence of valve involvement on imaging or blood cultures.
When to use this code
Use I33 when the provider documents acute or subacute endocarditis without naming a specific infective agent or when the record supports endocarditis but not a more detailed code. It also fits cases where the type is clearly stated as acute or subacute and no other subclassification is provided.
Do not use for
Do not use I33 for chronic endocarditis, noninfective endocarditis, or rheumatic valve disease unless documentation specifically supports acute or subacute endocarditis. Check documentation if the record names a specific organism or a different cardiac infection.
Coding tip
Code the most specific endocarditis diagnosis documented and verify whether the record supports an acute, subacute, or organism-specific code.