What does ICD-10 code Q21 mean?

ICD-10 code Q21 is the standardized code used for congenital malformations of cardiac septa in medical records and coding systems.

When is ICD-10 code Q21 used?

Doctors, hospitals, and insurers may use ICD-10 code Q21 when recording congenital malformations of cardiac septa in a standardized format. This entry may also act as a broader category that points toward more specific child codes.

Does ICD-10 code Q21 confirm a diagnosis?

No. A code helps standardize documentation and claims, but it should not be read as a substitute for a clinician's full assessment.

ICD10

ICD-10 Code Q21: Congenital malformations of cardiac septa

Name: ICD-10 Code Q21: Congenital malformations of cardiac septa
Creator: HealthAssure Clinical Team
Published: 2026-05-21T06:29:30.450Z

Q21 is an ICD-10 diagnosis entry used to group records related to Congenital malformations of cardiac septa. You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen. ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0).

Reviewed by HealthAssure Clinical TeamUpdated 21 May 2026

What is this code?

ICD-10 entries help standardize how diagnoses are organized for coding, reporting, analytics, and documentation. This code sits within the broader ICD-10 area for Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0).

When is it used?

May be used when a clinician documents congenital malformations of cardiac septa in a patient's medical record.
May appear in hospital records, claims, referrals, and clinical documentation.
This code may act more like a grouping or parent code, so a more specific child code may be used in final documentation when available.

What it does not mean

A code alone does not explain severity, treatment plan, or outcome.
A medical code should not be treated as a substitute for a doctor's diagnosis or advice.
This entry may represent a broader category rather than the most specific billable code.

Code hierarchy

chapter

17Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA0)

block

Q20-Q28Congenital malformations of the circulatory system

currentQ20-Q28

Official coding notes

Excludes1 (do not code together)

acquired cardiac septal defect (I51.0)

Where you may see this code

You may see this entry in coding references, medical records, or claims workflows when a broader diagnosis category is being reviewed before a more specific code is chosen.

Related specialists

Cardiologist

Sibling codes

Q20Congenital malformations of cardiac chambers and connections Q22Congenital malformations of pulmonary and tricuspid valves Q23Congenital malformations of aortic and mitral valves Q24Other congenital malformations of heart Q25Congenital malformations of great arteries Q26Congenital malformations of great veins Q27Other congenital malformations of peripheral vascular system Q28Other congenital malformations of circulatory system

Coding guidelines

Compatibility

Legacy code aligns to an official FY 2026 category. Frontend should resolve to the official category page and surface the billable child codes.

Legacy codes

Q21

Replacement codes

Q21.0 — Ventricular septal defectQ21.3 — Tetralogy of FallotQ21.4 — Aortopulmonary septal defectQ21.8 — Other congenital malformations of cardiac septaQ21.9 — Congenital malformation of cardiac septum, unspecified

Common synonyms

Congenital malformations of cardiac septa

Frequently asked questions

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from ICD-10. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.