ICD-10 Code I25.2: Old myocardial infarction coding guide

Key Takeaways

ICD-10 Code I25.2 (Old myocardial infarction) classifies a past MI that occurred more than 4 weeks (28 days) prior to the current encounter and presents no active symptoms.

I25.2 is a billable, specific ICD-10-CM code valid for reimbursement in FY 2026 and is classified under Chapter I25: Chronic ischemic heart disease.

The 4-week threshold separates I25.2 from acute MI codes (I21.x) and subsequent MI codes (I22.x): crossing that line with the wrong code triggers audit risk and claim denials.

Practice management software like Pabau helps cardiology and primary care teams apply ICD-10 codes accurately, reducing denials in cardiac rehab billing.

ICD-10 Code I25.2, titled “Old myocardial infarction,” classifies a past MI that a patient has experienced but which is no longer active or symptomatic at the time of the encounter. The CDC/NCHS ICD-10-CM web tool defines it as a past myocardial infarction diagnosed by ECG or other investigation, but currently presenting no symptoms.

This distinction matters clinically. The code does not indicate ongoing ischemia, active chest pain, or hemodynamic instability. It signals a healed infarct: structural evidence remains (often visible on ECG as Q-waves or imaging findings), but the patient has no current acute presentation requiring treatment for the MI itself.

The code sits under the I25 parent category (Chronic ischemic heart disease), which is important for accurate ICD-10-CM diagnosis coding in cardiovascular contexts and downstream medical billing accuracy. I25 itself is not billable; I25.2 is the specific, reportable subcode.

When to use ICD-10 Code I25.2: The 4-week threshold explained

The 4-week rule is the most important boundary in MI coding, and it is where most billing errors originate. The ICD-10-CM classification treats MI as acute for the first 28 days. Once that window closes, the infarct is classified as old (or healed), and I25.2 applies.

• Days 1-28 (acute phase): Use I21.x codes (Acute myocardial infarction), specifying site and type.
• Day 29 onward (healed/old phase): Use I25.2 if the MI no longer requires active treatment and presents no current symptoms.
• Subsequent MI within 4 weeks of an existing acute MI: Use I22.x (Subsequent myocardial infarction), not I25.2.
• ECG-only finding with no symptoms: I25.2 is appropriate when the investigation (ECG, imaging) shows evidence of a prior infarct but the patient has no active complaints.

A practical scenario: a patient presents for a routine cardiology follow-up visit 6 weeks after discharge from a STEMI admission, billed under an office visit level such as CPT Code 99214. The acute episode has resolved, no further MI treatment is being provided, and the ECG shows residual Q-waves. ICD-10 Code I25.2 is the correct code here.

Coding it as I21.x would misrepresent the clinical status and flag the claim for review.

Another common situation involves incidental ECG findings. A patient being evaluated for hypertension has an ECG showing Q-waves consistent with an old inferior MI, but reports no cardiac symptoms and has no prior cardiac history on record.

Under ICD-10-CM guidelines, I25.2 correctly captures this asymptomatic, investigation-based diagnosis. Practices managing patients with several cardiovascular comorbidities still need structured documentation workflows so each condition is captured clearly at the point of care.

I25.2 code hierarchy and related ICD-10 codes

Understanding where I25.2 sits in the hierarchy helps coders assign the right code when multiple cardiac conditions are present. The I25 parent code covers the full spectrum of chronic ischemic heart disease. Key subcodes relevant to cardiovascular coding include the following:

Practices that manage patients with multiple cardiovascular diagnoses benefit from structured documentation inside their electronic medical records (EMR) system. Pabau’s patient record management feature organizes comorbidities and past diagnoses so coders can select the accurate code from documented findings at each encounter, not from memory.

For coders who need to verify the current hierarchy and any FY 2026 updates, the AAPC Codify ICD-10-CM lookup provides searchable access to the tabular list with annotation back-references for all parent codes in the I25 category.

Documentation requirements for ICD-10 Code I25.2

The documentation burden for I25.2 is lower than for acute MI codes, but it is not zero. Coders need specific evidence in the record before assigning this code. Underdocumented encounters produce unspecified codes (I25.9), which carry less clinical weight and may affect risk adjustment in value-based care models.

For accurate ICD-10-CM diagnosis coding, the record must support the code being assigned. For I25.2, acceptable documentation includes any of the following:

• ECG findings: Q-waves or other changes consistent with prior MI, documented and interpreted by the treating clinician.
• Imaging evidence: Echocardiogram, cardiac MRI, or nuclear stress test showing a regional wall motion abnormality or perfusion defect consistent with healed infarction.
• Clinical history: A clearly documented past medical history of MI with date of event (allowing confirmation that more than 28 days have elapsed).
• Physician attestation: The treating provider must explicitly reference the old or healed MI in the encounter documentation. A coder cannot assign I25.2 based on an incidental finding alone without physician acknowledgment.

The ICD-10-CM Official Guidelines specify that diagnosis codes should reflect conditions that affect patient care, monitoring, or treatment at the current encounter. If the old MI is being managed (for example, as the qualifying diagnosis for cardiac rehabilitation), it affects the encounter and must be documented and coded accordingly.

Maintaining HIPAA-compliant documentation workflows, ideally backed by clinical documentation software built for practices, is essential when cardiac histories influence ongoing treatment decisions and billing. Every code assigned should have a traceable documentation trail in the patient record.

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Sequencing rules: Primary vs secondary diagnosis for I25.2

Whether I25.2 is coded as primary or secondary depends entirely on the reason for the encounter, and getting this wrong affects reimbursement and quality reporting.

When I25.2 is the principal diagnosis

I25.2 can serve as the principal diagnosis when the old MI is the main condition being evaluated at the encounter. This is uncommon in outpatient settings but occurs when a patient presents specifically for review of a previously diagnosed old MI (for example, a new patient who had a foreign MI and is establishing care).

When I25.2 is a secondary diagnosis

More commonly, I25.2 appears as an additional (secondary) diagnosis supporting the reason for the encounter. Typical scenarios include:

• Cardiac rehabilitation: I25.2 is listed as an additional diagnosis supporting eligibility for Phase II or III rehab services, with the rehab visit coded as the primary reason for the encounter.
• Comorbidity documentation: A patient seen for hypertension or diabetes has a documented old MI that affects their risk stratification. I25.2 is coded additionally to reflect the full clinical picture.
• Pre-operative cardiac risk assessment: The old MI is coded secondarily to the primary reason for the pre-operative visit.

The ICD-10-CM Official Guidelines make clear that secondary diagnoses should be coded when they affect patient management at the encounter. An old MI that influences drug selection (antiplatelet therapy, beta-blockers), rehabilitation decisions, or risk stratification clearly meets this threshold.

Using Pabau’s digital intake forms for cardiology patients creates structured fields for capturing cardiac history, including prior MI dates. This data flows directly into encounter documentation, giving coders the specificity they need without relying on verbal history at billing time.

I25.2 and Medicare cardiac rehabilitation billing

ICD-10 Code I25.2 is a qualifying diagnosis for Medicare Phase II cardiac rehabilitation coverage. This is one of its highest-stakes billing applications, and the CMS coverage article (A53775) specifically lists I25.2 among the approved diagnoses for cardiac rehab reimbursement.

Under Medicare, cardiac rehabilitation programs are covered for patients whose qualifying event or condition is documented and dated. For old MI patients, the documentation must confirm the infarct occurred more than 4 weeks before the rehabilitation services begin. Practices should have a process for confirming this threshold at intake, not at billing.

Key Medicare cardiac rehab coding points for I25.2:

• I25.2 must appear on the claim as a qualifying diagnosis, not merely in the progress notes.
• The referral or order for cardiac rehab should reference the specific qualifying condition (old MI).
• Medicare covers up to 36 sessions of Phase II cardiac rehab for qualifying diagnoses, with documentation supporting medical necessity at each session.
• If the patient also has coronary artery disease (I25.1x), code both. Dual coding does not disqualify the claim and gives a more complete clinical picture.

Practices using claims management software can validate diagnosis codes at the point of care, catching a misassigned code, like an acute MI billed past the 28-day window, before the claim goes out rather than during a remittance review or audit.

The ICD List reference database provides a quick-reference lookup for I25.2 alongside its approximate synonyms and inclusion terms, useful for verifying that the clinical terminology used in documentation maps to the correct code before submission.

Common coding errors and audit risk with I25.2

I25.2 is a low-complexity code conceptually, but it produces specific, recurring billing errors in practice. Recognizing these patterns helps coders and practice managers reduce denial rates before they accumulate, whether or not their medical billing software flags them automatically.

Error 1: Using I21.x past the 28-day window

The most common error. A patient is seen on day 35 post-MI and the coder assigns I21.09 (STEMI involving other coronary artery) out of habit from the discharge coding. The acute code is now incorrect.

This triggers claim review because the payer sees an acute MI code on a date well beyond the expected acute phase, raising questions about whether the visit is for a new event or an ongoing acute episode.

Error 2: Coding I25.9 instead of I25.2

When documentation clearly states “old myocardial infarction” or “history of MI with no current symptoms,” using I25.9 (unspecified) is a missed specificity error. Payers and risk adjustment models weight I25.2 differently from I25.9, and under HCC risk adjustment, specificity affects the patient’s risk score. Chronic disease management programs and cardiac rehab authorizations also require specific qualifying diagnoses, not unspecified codes.

Error 3: Omitting I25.2 when it is clinically relevant

The opposite problem: the old MI is documented but not coded because it is considered “just history.” Under ICD-10-CM Official Guidelines, conditions affecting patient management at the encounter must be coded. If the old MI informs the treatment plan (antiplatelet prescribing, exercise capacity limits, cardiac rehab eligibility), it belongs on the claim.

Using structured practice management software with problem-list features that flag past diagnoses during encounter documentation reduces omission errors, particularly when it’s clear who’s responsible for keeping records current across a care team.

Coders should not be working from a blank slate at each visit for established cardiac patients. Similarly, clinical documentation at your practice is stronger when patient history flows automatically from prior encounters rather than relying on re-entry at each visit.

The bottom line on I25.2 coding

The 4-week threshold defines the boundary between acute MI coding and ICD-10 Code I25.2, and crossing it carries financial and clinical consequences that surface in denied claims and revenue cycle disruption.

Misassigning an acute code past 28 days, using the unspecified I25.9 when documentation supports I25.2, or omitting the code entirely when it affects patient management all cost practices money and create audit exposure.

Pabau’s claims management software gives cardiology and primary care teams the tools to validate diagnosis codes, capture complete documentation at every encounter, and reduce the manual review burden that leads to these errors. To see how Pabau supports accurate cardiovascular coding workflows, book a demo with the team.

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