ICD-10 Code I21.A9 – Other myocardial infarction type (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.A9 – Other myocardial infarction type
What it is
I21.A9 identifies a myocardial infarction type that does not fit a more specific MI code. Use it for documented infarction categories that are not otherwise classified in ICD-10-CM.
Clinical signs
Clinical features vary; refer to documentation. Typical MI findings may include ischemic chest discomfort, dyspnea, ECG changes, or cardiac biomarker evidence, but you should code only what the record supports.
When to use this code
Use I21.A9 when the provider documents an acute myocardial infarction type that is not described by a more specific ICD-10-CM option. It is appropriate when the chart clearly names a qualifying “other” MI type and no better code is available.
If the note is vague, incomplete, or conflicts with another MI category, check documentation before assigning this code. Do not infer the infarction type from tests alone.
Do not use for
Do not use this code for a specific MI subtype that has its own ICD-10-CM code, or for a history of myocardial infarction. Check documentation if the record describes angina or another ischemic condition instead.
Coding tip
Verify the exact MI wording in the provider note and code the most specific documented type first.