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ICD-10-CM Q21.0: Ventricular septal defect

Q21.0 is the billable ICD-10-CM code for ventricular septal defect, in category Q21 (Congenital malformations of cardiac septa) of the Congenital malformations of the circulatory system section. As a principal diagnosis it groups to MS-DRG 306 Cardiac Congenital and Valvular Disorders with MCC, MS-DRG 307 Cardiac Congenital and Valvular Disorders without MCC (MDC 05 MDC 05: Diseases and Disorders of the Circulatory System); or MS-DRG 791 Prematurity with Major Problems, MS-DRG 793 Full Term Neonate with Major Problems (MDC 15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period). As a secondary diagnosis it is a CC, excluded with 89 principal diagnoses. 18 LCD billing and coding articles list it as covered.

Compiled from CMS files by the QuickIntell RCM Editorial Team · Data effective · Method: reference methodology · Report a data correction

Data currency: ICD-10-CM code descriptions: FY2027 (effective October 1, 2026); IPPS Table 5 (MS-DRG weights): v44 FY2027 (final rule + CN3) (effective October 1, 2026); ICD-10-CM to HCC mapping: PY2027 initial ICD-10-CM mappings (dates of service 2026) (payment year 2027); Medicare Coverage Database billing and coding articles: MCD release October 8, 2026 (effective October 4, 2026). Next CMS release: FY2028 code files, effective October 1, 2027 for the ICD-10-CM code descriptions; FY2028 final rule (August 2027), effective October 1, 2027; an April 1 interim grouper update when CMS issues one for the IPPS Table 5 (MS-DRG weights); PY2028 advance notice (February 2027) and the PY2027 midyear final mapping (spring 2027) for the ICD-10-CM to HCC mapping; weekly, every Thursday for the Medicare Coverage Database billing and coding articles.

Code
Q21.0
billable FY2027 ICD-10-CM code
Category
Q21 Congenital malformations of cardiac septa
Chapter
17: Congenital malformations, deformations, chromosomal abnormalities, and genetic disorders (Q00-QA1)
CC/MCC (MS-DRG v44)
CC
CMS-HCC V28
Not mapped
POA reporting
Exempt

Tabular list notes for Q21.0

The tabular list has no notes on Q21.0 itself; the notes below apply from its parent headings.

Inherited from Q21 (Congenital malformations of cardiac septa)

Excludes1 (never coded together)
  • acquired cardiac septal defect (I51.0)

MS-DRG grouping when Q21.0 is the principal diagnosis

MS-DRG v44 groups for Q21.0 as principal diagnosis
MDCMS-DRGs
05 MDC 05: Diseases and Disorders of the Circulatory System306307
15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period791793

The final group also depends on procedures, secondary diagnoses and discharge status; the MS-DRG lookup for Q21.0 shows the full grouping logic.

CC/MCC status and inpatient edits

As a secondary diagnosis, Q21.0 is a CC under MS-DRG v44, unless the principal diagnosis is one of the 89 codes in its exclusion list. Check Q21.0 against a principal diagnosis.

  • Present on admission: exempt from POA indicator reporting (FY2027 exempt list).

CMS-HCC V28 risk adjustment

Q21.0 does not map to a payment HCC in the PY2027 CMS-HCC V28 model, so on its own it does not change a Medicare Advantage risk score.

LCD billing and coding articles that list Q21.0

18 current Medicare billing and coding articles list Q21.0 among the diagnoses that support medical necessity for the services they cover.

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Frequently asked questions

What does ICD-10-CM Q21.0 mean?

Q21.0 means ventricular septal defect. It is one of 17 billable codes under Q21, congenital malformations of cardiac septa.

What can't be coded with Q21.0?

Excludes1 at Q21: acquired cardiac septal defect (I51.0). These are never reported together with Q21.0.

Which MS-DRG does Q21.0 group to?

As the principal diagnosis, Q21.0 groups to MS-DRG 306 Cardiac Congenital and Valvular Disorders with MCC, MS-DRG 307 Cardiac Congenital and Valvular Disorders without MCC (MDC 05 MDC 05: Diseases and Disorders of the Circulatory System); or MS-DRG 791 Prematurity with Major Problems, MS-DRG 793 Full Term Neonate with Major Problems (MDC 15 MDC 15: Newborns and Other Neonates with Conditions Originating in Perinatal Period) under MS-DRG v44, before procedures and secondary diagnoses are applied.

Is Q21.0 a CC or MCC?

Q21.0 is a CC under MS-DRG v44; 89 principal diagnoses exclude it.

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-10. Verify against the primary file before billing or contracting decisions. The reference methodology explains how each figure is computed from these files.

Disclaimer

The descriptor and notes are reproduced from the FY2027 ICD-10-CM files; MS-DRG, CC/MCC and HCC facts come from the CMS FY2027 and PY2027 tables. Code from the medical record and the ICD-10-CM Official Guidelines. Not legal, clinical or billing advice.

Found a figure that does not match the CMS file? Report a data correction with the CMS file and the value you expected; the request reaches the editorial team through the contact form.