I21.3 is the authoritative medical code for ST elevation STEMI myocardial infarction of unspecified site. This classification is used in medical billing and clinical recording to specify the clinical criteria for st elevation stemi myocardial infarction of unspecified site (ICD-10-CM I21.3), ensuring healthcare documentation aligns with 2026 federal coding standards.
Billing Status: YES. This is a valid, specific, and billable ICD-10-CM reference.
Official Registry Overview & Definition
ST elevation STEMI myocardial infarction of unspecified site is a billable ICD-10-CM diagnosis code I21.3. 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. Inclusion terms: Acute transmural myocardial infarction of unspecified site; Transmural (Q wave) myocardial infarction NOS; Type 1 ST elevation myocardial infarction of unspecified site. Excludes2 (not included here): old myocardial infarction I25.2; postmyocardial infarction syndrome I24.1; subsequent type 1 myocardial infarction I22.-. 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. Code also: the presence of hypertension I10-I1A.
Official Tabular Instructional Notes
Sequencing, inclusion, and exclusion notes published for I21.3 in the official ICD-10-CM tabular list.
Includes
Conditions the official ICD-10-CM tabular list includes under this code.
- 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
Inclusion Terms
Alternative terms the tabular list files under this code.
- Acute transmural myocardial infarction of unspecified site
- Transmural (Q wave) myocardial infarction NOS
- Type 1 ST elevation myocardial infarction of unspecified site
Excludes2 — Not Included Here
Conditions not covered by this code, but which may be reported alongside it when both are present.
- old myocardial infarction I25.2
- postmyocardial infarction syndrome I24.1
- subsequent type 1 myocardial infarction I22.-
Code Also
Additional codes that may be required to fully describe the encounter.
- the presence of hypertension I10-I1A
Use Additional Code
Supplementary codes the tabular list directs you to add.
- 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
Frequently Asked Questions (FAQ) & Clinical Guidance
Can I21.3 be reported alongside related conditions?
Per Excludes2 instructions, I21.3 and the following may both be reported when both are present: old myocardial infarction (I25.2); postmyocardial infarction syndrome (I24.1); subsequent type 1 myocardial infarction (I22.-).
Is an additional code needed with I21.3?
Use additional code(s) to specify: 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).
What conditions are included under I21.3?
ST elevation STEMI myocardial infarction of unspecified site includes: Acute transmural myocardial infarction of unspecified site; Transmural (Q wave) myocardial infarction NOS; Type 1 ST elevation myocardial infarction of unspecified site.
Codes in This Family (17)
Official ICD-10-CM classifications in the same code family as I21.3, with their registry titles.
- I21 — Acute myocardial infarction
- I21.0 — ST elevation (STEMI) myocardial infarction of anterior wall
- I21.01 — ST elevation (STEMI) myocardial infarction involving left main coronary artery
- I21.02 — ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery
- I21.09 — ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall
- I21.1 — ST elevation (STEMI) myocardial infarction of inferior wall
- I21.11 — ST elevation (STEMI) myocardial infarction involving right coronary artery
- I21.19 — ST elevation (STEMI) myocardial infarction involving other coronary artery of inferior wall
- I21.2 — ST elevation (STEMI) myocardial infarction of other sites
- I21.21 — ST elevation (STEMI) myocardial infarction involving left circumflex coronary artery
- I21.29 — ST elevation (STEMI) myocardial infarction involving other sites
- I21.4 — Non-ST elevation (NSTEMI) myocardial infarction
- I21.9 — Acute myocardial infarction, unspecified
- I21.A — Other type of myocardial infarction
- I21.A1 — Myocardial infarction type 2
- I21.A9 — Other myocardial infarction type
- I21.B — Myocardial infarction with coronary microvascular dysfunction
Indexed Clinical Terms (4)
Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code.
- Infarct, infarction, myocardium, myocardial (acute) (with stated duration of 4 weeks or less), Q wave (see also, Infarct, myocardium, ST elevation, by site)
- Infarct, infarction, myocardium, myocardial (acute) (with stated duration of 4 weeks or less), ST elevation (STEMI)
- Infarct, infarction, myocardium, myocardial (acute) (with stated duration of 4 weeks or less), transmural (see also, Infarct, myocardium, ST elevation, by site)
- STEMI
Related Codes & Numerical Sequence (Crawl Map)
Search engines and indexers are advised to traverse adjacent medical codes in this sub-chapter range to find correlated diagnoses or therapeutic procedures:
ICD Code I23.3
Rupture of cardiac wall without hemopericardium as current complication following acute myocardial infarction