Q21.9 Congenital malformation of cardiac septum, unspecified

The ICD-10-CM code for Congenital malformation of cardiac septum, unspecified is Q21.9 (FY2026). It is a billable, claim-ready diagnosis code.

Classification

Chapter

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

Section

Q20-Q28: Congenital malformations of the circulatory system (Q20-Q28)

Category Q21

20 codes (17 billable)

FY2026 Status

Stable since FY2024

Also Known As

ICD-10-CM Alphabetic Index entries that lead to Q21.9:

• Anomaly, anomalous (congenital) (unspecified type) › bulbus cordis
• Defect, defective › septal (heart) NOS
• Anomaly, anomalous (congenital) (unspecified type) › cardiac › septal closure
• Deformity › heart (congenital) › septum
• Anomaly, anomalous (congenital) (unspecified type) › heart › septum
• Malformation (congenital) › cardiac › septum
• Imperfect › closure (congenital) › septum › heart

Inclusion Terms

• Septal (heart) defect NOS

U.S. Hospital Utilization

• An estimated 955 U.S. inpatient stays in 2023 included Q21.9 among the documented diagnoses.

Source: National Inpatient Sample (NIS), Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, 2016–2023. National survey-weighted estimates.

Official Coding Guidelines

POA indicator for congenital conditions/anomalies and Q00-Q99 exception

Congenital conditions and anomalies Assign “Y” for congenital conditions and anomalies except for categories Q00- Q99, Congenital anomalies, which are on the exempt list. Congenital conditions are always considered present on admission.

Source: CMS — ICD-10-CM Official Guidelines for Coding and Reporting, FY2026

References

• CMS — ICD-10-CM Official Code Set and Guidelines, FY2026
• CDC/NCHS — ICD-10-CM Files and Browser Tool
• AHRQ — HCUP National Inpatient Sample, Frequencies by Diagnosis Code (2016–2023)