ICD-10 Code B33.21 – Viral endocarditis (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B33.21 – Viral endocarditis
What it is
Viral endocarditis is an infection or inflammation involving the heart’s inner lining or valves, attributed to a viral cause. Use this code when the record clearly documents viral endocarditis.
Clinical signs
Clinical features vary; refer to documentation. Records may note fever, new or changing heart murmur, embolic findings, or evidence of endocardial involvement linked to a viral infection.
When to use this code
Use B33.21 when the provider specifically diagnoses viral endocarditis and the chart supports that etiology. This code fits inpatient, outpatient, or consult notes that clearly state the condition. If the documentation only says endocarditis without a viral cause, check documentation before assigning this code.
Do not use for
Do not use this code for bacterial, fungal, or noninfective endocarditis. Also avoid it when the record mentions myocarditis, pericarditis, or endocarditis without confirming a viral cause.
Coding tip
Code the documented organism or cause exactly as stated, and query if the note does not clearly support a viral etiology.