ICD-10 Code I33.0 – Acute and subacute infective endocarditis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I33.0 – Acute and subacute infective endocarditis
What it is
I33.0 identifies infective endocarditis that develops quickly or over days to weeks. It involves infection of the heart’s inner lining or valves and requires documentation of an acute or subacute course.
Clinical signs
Common findings include fever, a new or changing heart murmur, and evidence of systemic infection. Clinical features vary; refer to documentation for valve involvement, embolic events, or microbiologic confirmation.
When to use this code
Use I33.0 when the provider documents acute or subacute infective endocarditis, including suspected valve infection supported by clinical assessment. You may also use it when the note clearly states infective endocarditis without a more specific organism or site code.
Check documentation if the record distinguishes acute from chronic endocarditis or names a different endocarditis type. Make sure the diagnosis is active and not just a history of prior infection.
Do not use for
Do not use this code for noninfective endocarditis or for a past history of endocarditis alone. If the documentation is nonspecific, check documentation before assigning I33.0.
Coding tip
Confirm that the provider describes the condition as acute or subacute and documents infective endocarditis, not merely a murmur or fever.