ICD-10-CM 2027
ICD-10 code for Subendocardial infarct
Non-ST elevation (NSTEMI) myocardial infarction
From the official ICD-10-CM alphabetic index entry “Infarct, infarction › subendocardial (acute) (nontransmural)”. Page updated September 29, 2026.
About coding Subendocardial infarct
The ICD-10-CM code for Subendocardial infarct is I21.4 (Non-ST elevation (NSTEMI) myocardial infarction).
Within I21 (acute myocardial infarction), I21.4 is specifically for Non-ST elevation (NSTEMI) myocardial infarction. Related codes cover 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), ST elevation (STEMI) myocardial infarction of unspecified site (I21.3), 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.
Common questions about Subendocardial infarct ICD-10 codes
What is the ICD-10 code for Subendocardial infarct?
- I21.4 — Non-ST elevation (NSTEMI) myocardial infarction.
Is I21.4 billable?
- Yes. I21.4 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can I21.4 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict I21.4 as a principal diagnosis.
Is I21.4 a CC or MCC?
- I21.4 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.