ICD-10 Code I35.1: Nonrheumatic aortic (valve) insufficiency

Key Takeaways

ICD-10 Code I35.1 remains a billable code in the FY2026 ICD-10-CM code set (October 1, 2025 – September 30, 2026), covering nonrheumatic aortic (valve) insufficiency.

Applicable To terms for I35.1 are aortic (valve) incompetence NOS and aortic (valve) regurgitation NOS — both map to I35.1 when etiology is nonrheumatic.

Never use I35.1 for rheumatic aortic valve disease: rheumatic etiology maps to I06.x, not the I35.x category. Provider documentation must confirm the distinction.

Pabau, practice management software with built-in claims management, helps cardiology and general practice billing teams keep diagnosis codes accurate and claims clean from the point of documentation.

ICD-10 Code I35.1 is the billable, specific ICD-10-CM diagnosis code for Nonrheumatic aortic (valve) insufficiency. It remains billable in the FY2026 ICD-10-CM code set maintained by CMS, effective October 1, 2025 through September 30, 2026.

ICD-10 Code I35.1: Definition and billability

The code has been part of ICD-10-CM since the original US implementation on October 1, 2015, and coders can use it as a standalone billable code to report this diagnosis for reimbursement purposes.

Aortic valve insufficiency occurs when the aortic valve fails to close properly, allowing blood to flow back into the left ventricle. When there is no documented rheumatic etiology, ICD-10 Code I35.1 is the correct assignment. The code falls within the I35 category of nonrheumatic aortic valve disorders, which sits inside the circulatory system chapter (I00-I99) of ICD-10-CM.

Applicable synonyms for I35.1: Aortic regurgitation and incompetence

Two clinical terms map to ICD-10 Code I35.1 when etiology is nonrheumatic. The Applicable To notes within ICD-10-CM confirm these are interchangeable for coding purposes, provided the physician has not documented a rheumatic cause.

• Aortic (valve) regurgitation NOS — backward flow of blood through the aortic valve; the most commonly used clinical term
• Aortic (valve) incompetence NOS — valve fails to seal completely; used interchangeably with regurgitation in cardiology documentation

“Aortic (valve) insufficiency” is not a third Applicable To synonym. It is I35.1’s own official descriptor, the term the code set uses as the code’s title rather than an alternate term mapped onto it.

“NOS” stands for “not otherwise specified.” When a physician documents aortic regurgitation without specifying rheumatic fever as the underlying cause, I35.1 is the correct assignment. Coders should not apply clinical judgment to determine etiology — that determination must come directly from provider documentation. Keeping this principle clear in your chart notes protects against audit risk.

Rheumatic vs nonrheumatic aortic valve disease: The critical coding distinction

The rheumatic vs nonrheumatic distinction is the most consequential coding decision for aortic valve insufficiency. Getting this wrong produces an incorrect code assignment with real reimbursement consequences.

Rheumatic aortic valve disease traces back to rheumatic fever, which causes scarring and structural damage through an autoimmune response. Nonrheumatic disease has other causes, including age-related degeneration, bicuspid aortic valve anatomy, infective endocarditis, aortic root dilatation, or connective tissue disorders such as Marfan syndrome.

Clinicians must document which applies, and coders must never infer etiology from clinical context alone. Etiology drives code selection elsewhere in ICD-10-CM too, as with M30.2.

When provider documentation is ambiguous, coders should query the provider rather than assign I35.1 by assumption. This querying practice is part of sound compliance documentation within any cardiology or general practice billing workflow.

I35 code category: Aortic valve codes at a glance

ICD-10 Code I35.1 sits within the I35 category, which covers all nonrheumatic aortic valve disorders. Knowing the full block helps coders select the most specific code and avoid unspecified or incorrect assignments.

A common error is assigning I35.0 (stenosis) when the documentation clearly states regurgitation or insufficiency. Always match the code to the precise valve abnormality described.

For concurrent stenosis and insufficiency, I35.2 is the correct code rather than reporting I35.0 and ICD-10 Code I35.1 separately. The I08.- block follows the same combined-valve logic on the multi-valve side, as seen in I08.2.

Excludes2 notes for I35.1: Related conditions you can still code separately

ICD-10 Code I35.1 carries several Excludes2 notes, not Excludes1. Excludes2 means “not included here”: the excluded condition is not part of what I35.1 represents, but the two conditions are distinct enough that both can be reported together when each is separately documented.

That is different from an Excludes1 note, which bars reporting both codes together under any circumstances.

The ICD-10-CM tabular list carries the following notes under category I35:

• Excludes2: Aortic valve disorder with diseases of mitral and/or tricuspid valve(s) (I08.-)
• Excludes2: Specified as congenital (Q23.0, Q23.1)
• Excludes2: Specified as rheumatic (I06.-)
• Code also: Bicuspid aortic valve (Q23.81), when documented

When documentation supports both nonrheumatic aortic insufficiency and a separately documented mitral, tricuspid, congenital, or rheumatic valve finding, coders can report both I35.1 and the matching additional code rather than assuming the pairing is automatically disallowed.

Confirm which code, or combination, the documentation actually supports before finalizing the claim. A mismatched Excludes2 pairing is a documentation question, not an automatic denial, though robust claims management workflows should still flag the combination for manual review before submission.

Documentation requirements for accurate aortic regurgitation ICD-10 coding

Accurate assignment of ICD-10 Code I35.1 depends entirely on what the provider documents. Four elements are non-negotiable for defensible code selection.

• Etiology confirmation: The note must state nonrheumatic, or it must exclude rheumatic fever as a cause. “Aortic regurgitation” alone, without etiology, is technically sufficient under ICD-10-CM guidelines for I35.1 because the Applicable To notes cover NOS presentations, but explicit etiology strengthens audit defensibility.
• Valve-specific diagnosis: Documentation should name the specific valve abnormality (insufficiency, regurgitation, or incompetence) rather than a generic “aortic valve disease” which could map to multiple codes.
• Severity grading: Mild, moderate, or severe grading does not change the code, but it supports medical necessity for associated procedures and affects DRG calculation when combined with additional diagnoses.
• Associated conditions: If the patient also has mitral or tricuspid valve disease, the documentation must make the clinical relationship clear. This determines whether I35.1, an I08.- code, or both apply.

Keeping documentation complete from the point of the clinical encounter reduces downstream coding queries. Digital clinical forms that prompt providers to confirm etiology fields can materially reduce the rate of ambiguous aortic valve documentation. The WHO’s ICD-10 classification supports this structured documentation approach globally.

Accurate coding starts with accurate documentation

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Common coding mistakes with aortic stenosis vs insufficiency

Several recurring errors appear across aortic valve code assignments. Catching them before claim submission prevents denials and avoids audit triggers.

• Using I35.1 for rheumatic disease: When the provider documents or implies rheumatic fever as the cause, I06.1 applies. Assigning I35.1 to a patient with documented rheumatic fever history misrepresents the clinical picture.
• Confusing I35.0 and I35.1: Stenosis (narrowing, I35.0) and insufficiency (backward flow, I35.1) are distinct conditions. Documentation review must identify which valve dysfunction is present, not which code appears nearest in the code set.
• Treating the I08.- Excludes2 note as an absolute bar: Excludes2 allows I35.1 and an I08.- code to be reported together when each condition is separately documented. Dropping one diagnosis without confirming the documentation, on the assumption the pairing is never allowed, is the actual mistake.
• Using I35.9 (unspecified) when specific documentation exists: When a provider has documented “aortic regurgitation” or “aortic incompetence,” I35.9 is not appropriate. The Applicable To notes for ICD-10 Code I35.1 explicitly capture those terms.
• Assuming etiology without provider documentation: A coder cannot determine rheumatic vs nonrheumatic status from the patient’s history alone. Provider documentation is the only valid basis for this distinction.

These patterns appear consistently across cardiology billing audits. Practices that have integrated EHR documentation workflows at the point of care see fewer query cycles between coding staff and providers. Specificity trade-offs like this are not unique to cardiology, as with H66.93 elsewhere in ICD-10-CM.

DRG groupings for I35.1: MS-DRG 306 vs 307

ICD-10 Code I35.1 does not carry a CC (Complication or Comorbidity) or MCC (Major Complication or Comorbidity) designation on its own. As a principal diagnosis, it groups to MS-DRG 306 (cardiac congenital and valvular disorders with MCC) or MS-DRG 307 (cardiac congenital and valvular disorders without MCC), under MS-DRG version 43.0, effective October 1, 2025 through September 30, 2026.

The 306/307 split is driven by other secondary diagnoses on the claim, not by I35.1 itself. If a qualifying MCC is documented and coded elsewhere on the same encounter, the case groups to DRG 306. Without one, it groups to DRG 307.

Coders should verify the exact DRG assignment against the current CMS MS-DRG Definitions Manual, since MDC and DRG logic can change with annual updates.

Billing teams managing cardiac admissions still benefit from structured coding workflows that catch CC/MCC pairings automatically during charge capture, since the MCC driving the DRG split usually comes from a comorbidity documented outside the diagnosis itself.

Related CPT procedure codes for aortic valve insufficiency

ICD-10 Code I35.1 commonly appears alongside CPT codes for aortic valve repair and replacement procedures. These pairings require payer-specific confirmation for medical necessity. The codes listed here are commonly associated but not mandatorily linked.

Always verify CPT-to-ICD pairings against the AAPC code reference and individual payer LCD/NCD policies before finalizing the claim. Payer requirements for TAVR (CPT 33361) in particular can vary significantly based on frailty scoring and multidisciplinary team documentation. Practices handling high volumes of cardiac claims benefit from structured patient care workflows that tie pre-authorization requirements to specific procedure-diagnosis pairings.

Conclusion

Coding aortic valve disease accurately comes down to one decision: rheumatic or nonrheumatic? When providers document nonrheumatic etiology, or document regurgitation, incompetence, or insufficiency without rheumatic fever, ICD-10 Code I35.1 is the specific, billable code. The Excludes2 notes and the I35.0/I35.2 distinctions handle the boundary conditions.

Practices that build documentation prompts into their clinical intake and charting workflows reduce query cycles and coding errors before claims reach the payer. Pabau’s AI-assisted clinical documentation tools help practitioners capture complete, structured notes at the point of care, so the etiology, severity, and associated conditions that coders need are always present in the record.

Cardiology practices, wellness clinics, and primary care teams all rely on the same principle: complete documentation up front prevents denials later. To see how Pabau supports accurate clinical documentation across specialties, book a demo.

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