2027 ICD-10-CM Diagnosis Code Q21.9Congenital malformation of cardiac septum, unspecified

ICD-10-CM Codes›Q00-Q99›Q20-Q28›Q21

ICD-10-CM Q21.9
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Q21.9 is a billable ICD-10-CM diagnosis code for congenital malformation of cardiac septum, unspecified. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 306 through 307. The code is exempt from POA reporting. Coders also document this condition as atresia of pulmonary artery with septal defect. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac and circulatory congenital anomalies.

Code Identity

ICD-10-CM Code
Q21.9
Billable Status
Yes — Valid for Submission
Code Describes
Congenital malformation of cardiac septum, unspecified
Short Description
Congenital malformation of cardiac septum, unspecified
Same as the full description in the CMS dataset.
Parent Code
Q21
Congenital malformations of cardiac septa

Code Classification

ChapterQ00-Q99Congenital malformations, deformations and chromosomal abnormalities
SectionQ20-Q28Congenital malformations of the circulatory system
CategoryQ21Congenital malformations of cardiac septa
This CodeQ21.9Congenital malformation of cardiac septum, unspecified

Present on Admission (POA)Billing

Q21.9 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Congenital malformations of the circulatory system (Q20-Q28).

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Atresia of pulmonary artery with septal defect
  • Cardiac septal defects
  • Congenital atresia of pulmonary artery
  • Congenital heart disease, septal and bulbar anomalies
  • Congenital septal defect of heart
  • Severe hypotonia, psychomotor developmental delay, strabismus, cardiac septal defect syndrome

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Q21.9: its own notes plus those printed at Q21 and Chapter 17. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • Septal (heart) defect NOS

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From Q21 Congenital malformations of cardiac septa applies to 17 codes
  • acquired cardiac septal defect (I51.0)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • inborn errors of metabolism (E70-E88)

Notes

General instructions on how these codes are used.

From Chapter 17 (Q00-QA1) Congenital malformations, deformations and chromosomal abnormalities applies to 900 codes
  • Codes from this chapter are not for use on maternal records

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Q21.9, its category, or a range that includes it.

Use Additional Code 1

These codes say to use an additional code from the note, and Q21.9 is one of the codes named.

  • Q87.88 CTNNB1 syndrome
    congenital heart malformations (Q20.0-Q24.9) names Q20.0-Q24.9, which includes this code

Code Also 1

These codes say Q21.9 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • Q87.85 MED13L syndrome
    congenital malformations of cardiac septa (Q21.-) names Q21.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

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.

Convert Q21.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
745.9 Septal closure anom NOS
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Q21.9Overview

What is the ICD-10 code for congenital malformation of cardiac septum, unspecified?

The ICD-10-CM code for congenital malformation of cardiac septum, unspecified is Q21.9 (sometimes written as Q219). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is Q21.9 (Congenital malformations of cardiac septa) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report congenital malformation of cardiac septum, unspecified on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does Q21.9 group to?

When congenital malformation of cardiac septum, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 306, 307, with relative weights from 0.9146 to 1.5457 depending on complications. Higher weights mean higher Medicare reimbursement.

Is Q21.9 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 congenital malformation of cardiac septum, unspecified on inpatient claims. The code appears in the Congenital malformations of the circulatory system (Q20-Q28) range of the CMS exempt list.

Can Q21.9 be reported with I51.0?

Not as a rule. The Excludes1 note at Q21, which applies to Q21.9, lists "acquired cardiac septal defect (I51.0)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).