ICD-10 Code I21.3 – ST elevation (STEMI) myocardial infarction of unspecified site (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.3 – ST elevation (STEMI) myocardial infarction of unspecified site
What it is
This code identifies an acute ST-elevation myocardial infarction when the infarct location is not documented or cannot be determined. Use it for a STEMI diagnosis without a specified wall, artery, or territory.
Clinical signs
Typical findings include acute chest pain or pressure, ischemic ECG changes with ST elevation, and evidence of myocardial injury. Clinical features vary; refer to documentation.
When to use this code
Use I21.3 when the record clearly states STEMI but does not name the affected site. It also fits cases where the provider documents an unspecified myocardial infarction location after evaluation. If a more specific STEMI site is documented, code that instead.
Do not use for
Do not use this code for NSTEMI, old myocardial infarction, or chest pain without confirmed infarction. Check documentation if the record describes a different MI type or a more specific site.
Coding tip
Query for the infarct location when STEMI is documented but the site is missing, because a specific code is preferred whenever supported.