Myocardial Infarction ICD-10-CM Codes

Explore ICD-10-CM codes for myocardial infarction, including STEMI, NSTEMI, initial and subsequent MIs, with coding tips for accurate documentation.

By Ericka Pingol on Aug 8, 2025.

Fact Checked by Gale Alagos.

Use Code

What ICD-10 codes are used for myocardial infarction?

Myocardial Infarction, commonly known as a heart attack, occurs when blood flow to a part of the heart is blocked. Here are the widely used Myocardial Infarction ICD codes:

I21.01: ST elevation (STEMI) myocardial infarction involving left main coronary artery: Used for an acute STEMI event specifically affecting the left main coronary artery, typically requiring immediate intervention due to its critical blood supply role.
I21.02: ST elevation (STEMI) myocardial infarction involving left anterior descending coronary artery: Used for STEMI cases involving the LAD artery, which supplies the front part of the heart and is often linked with anterior wall infarctions.
I21.09: ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall: Applies to anterior STEMI involving coronary arteries other than the left main or LAD, such as diagonal branches.
I21.11: ST elevation (STEMI) myocardial infarction involving right coronary artery: Used for inferior wall STEMI involving the right coronary artery, commonly seen with changes in the inferior ECG leads.
I21.19: ST elevation (STEMI) myocardial infarction involving other coronary artery of inferior wall: Applies to inferior wall STEMI involving arteries other than the RCA, such as the posterior descending artery.
I21.21: ST elevation (STEMI) myocardial infarction involving left circumflex coronary artery
Used for STEMI affecting the left circumflex artery, which typically supplies the lateral or posterior heart walls.
I21.29: ST elevation (STEMI) myocardial infarction involving other sites: Used when the STEMI affects other, less commonly specified coronary territories.
I21.3: ST elevation (STEMI) myocardial infarction, unspecified site: Used when STEMI is confirmed but the specific affected area or artery is not documented.
I21.4: Non-ST elevation (NSTEMI) myocardial infarction
Used for NSTEMI cases, where ECG does not show ST elevation but cardiac enzymes indicate myocardial damage.
I21.9: Acute myocardial infarction, unspecified: Used when there is insufficient detail to specify whether the MI is STEMI or NSTEMI or to identify the location.

Which myocardial infarction ICD codes are billable?

All ICD-10-CM myocardial infarction (MI) codes in the I21 and I22 categories are billable—as long as they are fully specified with the type (STEMI or NSTEMI), site (if known), and whether it’s an initial or subsequent episode.

Clinical information

A myocardial infarction (MI) occurs when blood flow to the heart muscle is abruptly blocked, most often due to coronary thrombosis or coronary embolism. This blockage deprives the myocardium of oxygen, resulting in infarction—the death of heart tissue.
The most common cause is a ruptured atherosclerotic plaque that triggers clot formation and leads to occlusion of a coronary artery. In rare and severe cases, complications such as coronary rupture may occur, significantly increasing the risk of mortality.
The affected area can vary, with damage often occurring in the left or right ventricle, depending on which artery is blocked. An infarction involving the ventricle myocardial region, such as the anterior wall of the left ventricle, is typically due to blockage in the left anterior descending artery.
MIs are classified as either ST elevation myocardial infarction (STEMI) or non-ST elevation myocardial infarction (NSTEMI) based on ECG findings.
A subsequent myocardial infarction refers to a new infarction occurring within four weeks of a previous one and may be further classified as a subsequent ST elevation STEMI if ECG changes are present. These distinctions are important for both clinical management and ICD-10-CM coding.
Outcomes vary depending on the severity and response time. In some cases, the patient may experience an acute myocardial infarction and expire before or during hospitalisation. In others, patients are stabilised and discharged alive after successful treatment, often with secondary prevention strategies in place.
Accurate documentation of events such as acute myocardial infarction discharged or thrombosis infarction supports ongoing care, quality reporting, and reimbursement.

Synonyms include:

Heart attack
Acute coronary syndrome
Coronary thrombosis
Cardiac infarction
Acute myocardial ischemia
Ventricle myocardial infarction

Commonly asked questions

The general ICD-10-CM code for myocardial infarction is I21, which includes both ST elevation (STEMI) and non-ST elevation (NSTEMI) types. Specific subcodes like I21.4 (NSTEMI) or I21.3 (STEMI, unspecified site) should be used based on the clinical presentation.

The ICD-10-CM code for unspecified infarction is I21.9: Acute myocardial infarction, unspecified. This is used when the type or location of the MI has not been clearly documented.

Acute myocardial infarction (AMI) refers to a sudden and severe blockage of blood flow to part of the heart muscle, usually caused by a thrombus or embolus in a coronary artery. This blockage deprives the heart tissue of oxygen, leading to ischemia and eventual infarction, or tissue death, if not treated promptly.

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