ICD-10 Code I21 – Acute myocardial infarction (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21 – Acute myocardial infarction
What it is
I21 identifies an acute myocardial infarction, meaning recent death of heart muscle from interrupted blood flow. Use it when the record clearly documents an acute MI.
Clinical signs
Typical findings include chest pain or pressure, shortness of breath, sweating, nausea, or other ischemic symptoms. ECG changes, cardiac biomarkers, and imaging may support the diagnosis; clinical features vary, refer to documentation.
When to use this code
Use I21 when the provider documents an acute myocardial infarction, including STEMI or NSTEMI, and the episode is current. Code it from the final or confirmed diagnosis, not from suspicion alone. If the record specifies the infarct site or type, follow the more specific I21 subcode.
Do not use for
Do not use I21 for old, healed, or history-only myocardial infarction. Avoid it when documentation only says chest pain, ischemia, or elevated cardiac markers without a confirmed acute MI.
Coding tip
Check the provider’s final diagnosis wording carefully and code the most specific acute MI type and site documented.