What is ICD-10 code I42.1?

I42.1 is the ICD-10-CM diagnosis code for Obstructive hypertrophic cardiomyopathy. A condition where the heart muscle becomes abnormally thick, particularly in the wall between the two lower chambers, which can obstruct blood flow out of the heart. I42.1 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. I42.1 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. I42.1 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. I42.1 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

What is the V28 vs V24 difference for I42.1?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For I42.1, V28 maps to Cardiomyopathy at RAF 0.339 while V24 mapped to Congestive Heart Failure at RAF 0.368. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting I42.1?

Document whether the patient has symptoms such as chest pain, shortness of breath, or syncope Note any family history of sudden cardiac death or hypertrophic cardiomyopathy Because I42.1 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

I42.1 ICD-10 Code: Obstructive hypertrophic

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupI42.1Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the circulatory system (I00-I99) / Other forms of heart disease (I30-I5A)

I42.1

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Obstructive hypertrophic cardiomyopathy

A condition where the heart muscle becomes abnormally thick, particularly in the wall between the two lower chambers, which can obstruct blood flow out of the heart.

Buddy Insight

Obstructive hypertrophic cardiomyopathy is a genetic heart condition causing asymmetric thickening of the interventricular septum that obstructs left ventricular outflow.

CMS-HCC V28

Mapped

HCC 227

Cardiomyopathy

RAF 0.339

CMS-HCC V24

Mapped

HCC 85

Congestive Heart Failure

RAF 0.368

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 85

Congestive Heart Failure

RAF 0.0

RXHCC

Mapped

HCC 186

Heart Failure

RAF 0.0

Code Trumping

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Code Book Path

Official

I42Cardiomyopathy

I42.1Obstructive hypertrophic cardiomyopathy

Inclusion Terms

Official

Hypertrophic subaortic stenosis (idiopathic)

Excludes 2

Official

ischemic cardiomyopathy (I25.5)
peripartum cardiomyopathy (O90.3)
ventricular hypertrophy (I51.7)

Related Child Codes

Official

I42.0Dilated cardiomyopathy

I42.2Other hypertrophic cardiomyopathy

I42.3Endomyocardial (eosinophilic) disease

I42.4Endocardial fibroelastosis

I42.5Other restrictive cardiomyopathy

Includes

Official

myocardiopathy

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for I42.1 in this effective period.

Code First

Official

pre-existing cardiomyopathy complicating pregnancy and puerperium (O99.4)

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for I42.1 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for I42.1 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Provider diagnosis of obstructive hypertrophic cardiomyopathy

Echocardiographic findings showing asymmetric septal hypertrophy with left ventricular outflow tract obstruction

Left ventricular outflow tract gradient documented

Family history of hypertrophic cardiomyopathy or sudden cardiac death

MEAT Support

HCC Buddy guidance

Provider diagnosis of obstructive hypertrophic cardiomyopathy

Echocardiographic findings showing asymmetric septal hypertrophy with left ventricular outflow tract obstruction

Left ventricular outflow tract gradient documented

Family history of hypertrophic cardiomyopathy or sudden cardiac death

Audit Caution

HCC Buddy guidance

Confusing obstructive with non-obstructive hypertrophic cardiomyopathy — the obstruction distinction is critical (I42.1 vs I42.2)

Coding hypertensive heart disease as hypertrophic cardiomyopathy — these are different conditions

Not coding associated arrhythmias or complications separately

Failing to document the obstruction gradient, which differentiates I42.1 from I42.2

Common Mistakes

HCC Buddy guidance

I42.2 — Other hypertrophic cardiomyopathy; non-obstructive form without outflow tract obstruction

I42.0 — Dilated cardiomyopathy; enlarged and weakened heart, not thickened

I11.0 — Hypertensive heart disease with heart failure; hypertensive cardiac hypertrophy is different

I42.9 — Cardiomyopathy, unspecified; use only when the type is not documented

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is I42.1 an HCC code?

Yes. I42.1 maps to Cardiomyopathy under the CMS-HCC V28 risk adjustment model (and Congestive Heart Failure under V24).

HCC Category Mapping

V28HCC 227, Cardiomyopathy

0.339

V24HCC 85, Congestive Heart Failure

0.368

ESRDHCC 85, Congestive Heart Failure

0.000

RxHCCHCC 186, Heart Failure

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for I42.1

For I42.1to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed I42.1 during that encounter, not just copy-forwarded from a problem list.

What This Code Means

I42.1 is the ICD-10-CM diagnosis code for obstructive hypertrophic cardiomyopathy. A condition where the heart muscle becomes abnormally thick, particularly in the wall between the two lower chambers, which can obstruct blood flow out of the heart. I42.1 sits in the ICD-10-CM chapter for diseases of the circulatory system (i00-i99), within the section covering other forms of heart disease (i30-i5a).

Under the CMS-HCC V28 risk adjustment model, I42.1 maps to Cardiomyopathy (HCC 227) with a community, non-dual, aged base RAF weight of 0.339. Under the older CMS-HCC V24 model, I42.1 maps to Congestive Heart Failure (HCC 85) with a community, non-dual, aged base RAF weight of 0.368. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Document whether the patient has symptoms such as chest pain, shortness of breath, or syncope. Because I42.1 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for I42.1 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Document whether the patient has symptoms such as chest pain, shortness of breath, or syncope
•Note any family history of sudden cardiac death or hypertrophic cardiomyopathy

Clinical Significance

Obstructive hypertrophic cardiomyopathy is a genetic heart condition causing asymmetric thickening of the interventricular septum that obstructs left ventricular outflow. It is the most common cause of sudden cardiac death in young athletes. This condition requires lifelong monitoring, activity restrictions, and may necessitate septal reduction therapy or implantable cardioverter defibrillator placement.

Documentation Requirements

✓Provider diagnosis of obstructive hypertrophic cardiomyopathy
✓Echocardiographic findings showing asymmetric septal hypertrophy with left ventricular outflow tract obstruction
✓Left ventricular outflow tract gradient documented
✓Family history of hypertrophic cardiomyopathy or sudden cardiac death
✓Symptoms (exertional dyspnea, syncope, chest pain) and functional status

Commonly Confused Codes

•I42.2: Other hypertrophic cardiomyopathy; non-obstructive form without outflow tract obstruction
•I42.0: Dilated cardiomyopathy; enlarged and weakened heart, not thickened
•I11.0: Hypertensive heart disease with heart failure; hypertensive cardiac hypertrophy is different
•I42.9: Cardiomyopathy, unspecified; use only when the type is not documented