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ICD-10-CM 2027 diagnosis code

Q21Congenital malformations of cardiac septa

Not billable — use a more specific code

Q21 is a header code, so it can't be reported by itself. Choose one of the 7 more specific codes beneath it.

Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data

About Q21

Q21 is the ICD-10-CM diagnosis code for congenital malformations of cardiac septa. It belongs to block Q20-Q28 (congenital malformations of the circulatory system) and chapter 17 (congenital malformations, deformations, chromosomal abnormalities, and genetic disorders). It is a header code, so it can't be reported by itself; one of its 7 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: Q21.0 (defect), Q21.1 (defect), Q21.2 (defect), Q21.3 (fallot), Q21.4 (defect), Q21.8 (septa) and Q21.9 (unspecified).

Don't report Q21 together with the conditions in its Excludes1 note: acquired cardiac septal defect (I51.0).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under Q21

Coding notes

Excludes1Not coded here — never report together with this code
  • acquired cardiac septal defect (I51.0)

Notes that apply from higher levels

Instructions written at a parent level also apply to Q21.

Broader instructions also apply from Chapter 17: Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders.

Codes whose notes reference Q21

Code history

  1. 2016
  2. 2017
  3. 2018
  4. 2019
  5. 2020
  6. 2021
  7. 2022
  8. 2023
  9. 2024
  10. 2025
  11. 2026
  12. 2027
  • FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
  • No changes since FY2016.

Common questions about Q21

Is Q21 billable?

No. Q21 is a header code. Report one of its more specific subcodes instead.