ICD-10 Code I21.B – Myocardial infarction with coronary microvascular dysfunction (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.B – Myocardial infarction with coronary microvascular dysfunction
What it is
This code identifies an acute myocardial infarction occurring with coronary microvascular dysfunction. Use it when the documentation links the infarction to abnormal small-vessel coronary circulation rather than a large epicardial artery lesion.
Clinical signs
Typical findings include ischemic chest pain, ECG changes, and evidence of myocardial injury consistent with infarction. Clinical features vary; refer to documentation for confirmation of coronary microvascular dysfunction.
When to use this code
Use I21.B when the provider documents myocardial infarction together with coronary microvascular dysfunction, including cases described as microvascular ischemia with infarction. You should code it from the record, not from suspicion alone. If the note does not clearly connect the infarction to microvascular dysfunction, check documentation.
Do not use for
Do not use this code for myocardial infarction without documented coronary microvascular dysfunction. Do not assign it for angina, ischemia, or microvascular dysfunction by itself.
Coding tip
Look for explicit provider wording tying the infarction to coronary microvascular dysfunction before assigning I21.B.