ICD-10-CM 2027 diagnosis code
I21.3ST elevation (STEMI) myocardial infarction of unspecified site
I21.3 is a valid, billable ICD-10-CM code for st elevation (stemi) myocardial infarction of unspecified site. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.Short description: ST elevation (STEMI) myocardial infarction of unsp site
Looking up by condition? See ICD-10 code for STEMI.
Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About I21.3
I21.3 is the ICD-10-CM diagnosis code for ST elevation (STEMI) myocardial infarction of unspecified site. It belongs to category I21 (acute myocardial infarction), block I20-I25 (ischemic heart diseases) and chapter 9 (diseases of the circulatory system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within I21, choose I21.3 (ST elevation (STEMI) myocardial infarction of unspecified site) only when documentation doesn't support a more specific option: ST elevation (STEMI) myocardial infarction of anterior wall (I21.0), ST elevation (STEMI) myocardial infarction of inferior wall (I21.1), ST elevation (STEMI) myocardial infarction of other sites (I21.2), Non-ST elevation (NSTEMI) myocardial infarction (I21.4), unspecified (I21.9), other type of myocardial infarction (I21.A) and myocardial infarction with coronary microvascular dysfunction (I21.B).
Use an additional 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.-) and 1 more.
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 280 (Acute Myocardial Infarction, Discharged Alive with MCC, relative weight 1.6112), DRG 281 (Acute Myocardial Infarction, Discharged Alive with CC, relative weight 0.9184), DRG 282 (Acute Myocardial Infarction, Discharged Alive without CC/MCC, relative weight 0.7378), DRG 283 (Acute Myocardial Infarction, Expired with MCC, relative weight 1.9619), DRG 284 (Acute Myocardial Infarction, Expired with CC, relative weight 0.7525) and DRG 285 (Acute Myocardial Infarction, Expired without CC/MCC, relative weight 0.539), in MDC 05 (Diseases and Disorders of the Circulatory System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Before ICD-10, this condition was coded in ICD-9-CM as 410.91 (acute myocardial infarction of unspecified site, initial episode of care).
Coding notes
- Acute transmural myocardial infarction of unspecified site
- Transmural (Q wave) myocardial infarction NOS
- Type 1 ST elevation myocardial infarction of unspecified site
Notes that apply from higher levels
Instructions written at a parent level also apply to I21.3.
› From I21 Acute myocardial infarction
- 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
- 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)
Broader instructions also apply from I20-I25 Ischemic heart diseases and Chapter 9: Diseases of the circulatory system.
Alphabetic index entries
4 entriesTerms in the official ICD-10-CM index that lead to I21.3.
- 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
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 05 · Diseases and Disorders of the Circulatory System
- 280Acute Myocardial Infarction, Discharged Alive with MCCRW 1.6112
- 281Acute Myocardial Infarction, Discharged Alive with CCRW 0.9184
- 282Acute Myocardial Infarction, Discharged Alive without CC/MCCRW 0.7378
- 283Acute Myocardial Infarction, Expired with MCCRW 1.9619
- 284Acute Myocardial Infarction, Expired with CCRW 0.7525
- 285Acute Myocardial Infarction, Expired without CC/MCCRW 0.539
ICD-9-CM equivalent
Converter →- 410.91Acute myocardial infarction of unspecified site, initial episode of careapproximate
From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about I21.3
Is I21.3 billable?
- Yes. I21.3 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can I21.3 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict I21.3 as a principal diagnosis.
Is I21.3 a CC or MCC?
- I21.3 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.
What DRG does I21.3 group to?
- I21.3 is used in the MS-DRG v44.0 logic for MS-DRG 280 (Acute Myocardial Infarction, Discharged Alive with MCC), MS-DRG 281 (Acute Myocardial Infarction, Discharged Alive with CC), MS-DRG 282 (Acute Myocardial Infarction, Discharged Alive without CC/MCC), MS-DRG 283 (Acute Myocardial Infarction, Expired with MCC), MS-DRG 284 (Acute Myocardial Infarction, Expired with CC) and MS-DRG 285 (Acute Myocardial Infarction, Expired without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.
What is the ICD-9 code for I21.3?
- The CMS General Equivalence Mappings map I21.3 to ICD-9-CM 410.91.