I21
Non-Billable (Header)Acute myocardial infarction
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
What This Code Means
I21 is the ICD-10-CM diagnosis code for acute myocardial infarction. I21 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering ischemic heart diseases (i20-i25).
Header codes like I21 cannot be reported on claims directly — they organize child codes that share clinical context but the actual diagnosis must be coded to the highest level of specificity supported by the documentation. Coders should look at I21's child codes and select the one that matches the patient's documented presentation, since payers reject header codes submitted as the primary diagnosis. For risk adjustment workflows, header codes never contribute to a Medicare Advantage member's RAF score on their own; only billable child codes that happen to map to a payment HCC affect risk-adjusted plan payments.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I21 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Includes
- cardiac infarction
- coronary (artery) embolism
- coronary (artery) occlusion
- coronary (artery) rupture
- coronary (artery) thrombosis
- infarction of heart, myocardium, or ventricle
- myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset
Excludes 2 — Not included here, may code separately
Use Additional Code
- code, if applicable, to identify:
- exposure to environmental tobacco smoke (Z77.22)
- history of tobacco dependence (Z87.891)
- occupational exposure to environmental tobacco smoke (Z57.31)
- status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
- tobacco dependence (F17.-)
- tobacco use (Z72.0)