2026 ICD-10-CM Diagnosis Code Q21.20Atrioventricular septal defect, unspecified as to partial or complete

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.20
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Q21.20 is a billable ICD-10-CM diagnosis code for atrioventricular septal defect, unspecified as to partial or complete. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 306 through 307. The code is exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Code Identity

ICD-10-CM Code
Q21.20
Billable Status
Yes — Valid for Submission
Code Describes
Atrioventricular septal defect, unspecified as to partial or complete
Short Description
Atrioventricular septal defect, unsp as to part or complete
Parent Code
Q21.2
Atrioventricular septal defect

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ20-Q28Congenital malformations of the circulatory system
CategoryQ21Congenital malformations of cardiac septa
This CodeQ21.20Atrioventricular septal defect, unspecified as to partial or complete

Present on Admission (POA)Billing

Q21.20 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Abnormality of atrioventricular valve leaflet in atrioventricular septal defect
  • Atrioventricular septal defect - isolated atrial component
  • Atrioventricular septal defect - isolated ventricular component
  • Atrioventricular septal defect - ventricular component
  • Atrioventricular septal defect - ventricular component under inferior bridging leaflet
  • Atrioventricular septal defect - ventricular component under superior bridging leaflet
  • Atrioventricular septal defect associated with tetralogy of Fallot
  • Atrioventricular septal defect with additional muscular ventricular septal defect
  • Atrioventricular septal defect with atrial and ventricular components and separate atrioventricular valves
  • Atrioventricular septal defect with atrioventricular valve regurgitation
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left inferior bridging leaflet lateral mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left septal commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through left superior bridging leaflet lateral mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right anterosuperior inferior mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right anterosuperior superior bridging leaflet commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right inferior bridging leaflet inferior mural commissure
  • Atrioventricular septal defect with atrioventricular valve regurgitation through right septal commissure
  • Atrioventricular septal defect with balanced ventricles
  • Atrioventricular septal defect with restrictive ventricular component
  • Atrioventricular septal defect with separate atrioventricular orifices
  • Atrioventricular septal defect with ventricular component and interchordal shunting under inferior bridging leaflet
  • Atrioventricular septal defect with ventricular component and interchordal shunting under superior bridging leaflet
  • Atrioventricular septal defect with ventricular component and shunting under connecting tongue with separate orifices
  • Atrioventricular septal defect with ventricular component under free floating superior bridging leaflet and chords to papillary muscle at right ventricular free wall
  • Atrioventricular septal defect with ventricular component under inferior bridging leaflet with chords to crest ventricular septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet with chords at crest ventricular septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet with chords to papillary muscle on right ventricular side septum
  • Atrioventricular septal defect with ventricular component under superior bridging leaflet without chordal attachment to ventricular septal crest
  • Atrioventricular septal defect with ventricular imbalance
  • Atrioventricular septal defect with ventricular imbalance consisting of dominant left ventricle and hypoplastic right ventricle
  • Atrioventricular septal defect with ventricular imbalance consisting of dominant right ventricle and hypoplastic left ventricle
  • Atrioventricular septal defect, blepharophimosis, radial and anal defect syndrome
  • Atrioventricular septal defect: atrial and ventricular components
  • Common atrioventricular canal
  • Common atrioventricular-type ventricular septal defect
  • Common atrium
  • Congenital abnormality of atrioventricular valve leaflet in atrioventricular septal defect
  • Congenital abnormality of atrioventricular valve papillary muscle in atrioventricular septal defect
  • Congenital abnormality of atrioventricular valves in atrioventricular septal defect
  • Congenital atrioventricular septal defect
  • Deficiency of atrioventricular valve leaflet in atrioventricular septal defect
  • Endocardial cushion defect
  • Fenestration of atrioventricular valve leaflet in atrioventricular septal defect
  • Flail atrioventricular valve leaflet in atrioventricular septal defect
  • Gelatinous atrioventricular valve leaflet in atrioventricular septal defect
  • Mass associated with atrioventricular valve leaflet in atrioventricular septal defect
  • Noncoapting atrioventricular valve leaflet in atrioventricular septal defect
  • Ostium primum defect
  • Residual interatrial communication
  • Spontaneous closure of atrial component of atrioventricular septal defect
  • Spontaneous closure of ventricular component of atrioventricular septal defect
  • Spontaneous closure of ventricular septal defect
  • Spontaneous closure of ventricular septal defect due to accessory tissue of atrioventricular valve
  • Thickened atrioventricular valve leaflet in atrioventricular septal defect
  • Ventricular imbalance

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Atrioventricular canal, NOS
  • Endocardial cushion defect NOS
  • Ostium primum atrial septal defect (type I) NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Canal
      • atrioventricular
    • Defect, defective
      • atrial septal
        • ostium primum type (type I)
    • Defect, defective
      • atrioventricular
        • canal
    • Defect, defective
      • atrioventricular
        • septal
          • unspecified as to partial or complete
    • Defect, defective
      • atrioventricular
        • septum
    • Defect, defective
      • cushion, endocardial
    • Defect, defective
      • ostium
        • primum
    • Endocardium, endocardial
      • cushion defect
    • Imperfect
      • closure (congenital)
        • atrioventricular ostium
    • Ostium
      • primum (arteriosum) (defect) (persistent)
    • Persistence, persistent(congenital)
      • atrioventricular canal
    • Persistence, persistent(congenital)
      • ostium
        • primum
    • Single
      • atrium

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MAL001
Cardiac and circulatory congenital anomalies
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Ostium Primum Defect

    a congenital defect in the atrial septum at the level of the atrioventricular valves, resulting in abnormalities in the mitral and/or tricuspid valve; this defect is most commonly seen in those with trisomy 21.

Patient EducationClinical

Congenital Heart Defects

Congenital heart defects (CHDs) are problems with the structure of the heart. "Congenital" means that that the problems are present at birth. These defects happen when a fetus's heart doesn't develop normally during pregnancy. Congenital heart defects are the most common type of birth defect.

The full article covers:

  • What are congenital heart defects?
  • What causes congenital heart defects?
  • Who is more likely to have a baby with a congenital heart defect?
  • What are the symptoms of congenital heart defects?
  • What other problems do congenital heart defects cause?
  • How are congenital heart defects diagnosed?
  • What are the treatments for congenital heart defects?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code History & ChangesHistory

Replacement Q21.20 replaces the following previously assigned code(s):

  • Q21.2 - Atrioventricular septal defect
FY 2023AddedAdded to the ICD-10-CM code setEffective October 1, 2022.
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Q21.20Overview

Is Q21.20 (Atrioventricular septal defect) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report atrioventricular septal defect, unspecified as to partial or complete on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does Q21.20 group to?

When atrioventricular septal defect, unspecified as to partial or complete is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9132 to 1.5758 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q21.20 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for atrioventricular septal defect, unspecified as to partial or complete on inpatient claims.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.