ICD-10 Code I21.9 – Acute myocardial infarction, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.9 – Acute myocardial infarction, unspecified
What it is
I21.9 identifies an acute myocardial infarction when the record confirms a heart attack but does not specify the affected wall, artery, or type. Use it only when documentation supports an acute MI and no more specific code is available.
Clinical signs
Typical findings include acute chest discomfort, ischemic ECG changes, and evidence of myocardial injury. Clinical features vary; refer to documentation.
When to use this code
Use I21.9 when the provider documents an acute myocardial infarction but the chart does not identify a more specific site or type. It may fit early encounters, incomplete reports, or transferred records where details are not yet finalized. Verify that the diagnosis is current and acute.
Do not use for
Do not use this code for old or prior myocardial infarction, unstable angina, or other ischemic heart disease without acute infarction. If the documentation names a more specific MI code, choose that code instead.
Coding tip
Code from the provider’s exact wording and query if the infarct location or type is documented elsewhere.