Congenital malformations of cardiac septa (Q21) ICD-10-CM
The Q21 code range covers congenital malformations of cardiac septa with 20 ICD-10-CM diagnosis codes. 17 of them are billable and valid for claim submission in fiscal year 2026, and the category headers group them but cannot themselves be billed.
Type 1 Excludes
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
- acquired cardiac septal defect I51.0
Codes in the Q21 Range 20 codes · 17 billable
- Q21 Congenital malformations of cardiac septaNon-billable
- Q21.0 Ventricular septal defect
- Q21.1 Atrial septal defectNon-billable
- Q21.10 Atrial septal defect, unspecified
- Q21.11 Secundum atrial septal defect
- Q21.12 Patent foramen ovale
- Q21.13 Coronary sinus atrial septal defect
- Q21.14 Superior sinus venosus atrial septal defect
- Q21.15 Inferior sinus venosus atrial septal defect
- Q21.16 Sinus venosus atrial septal defect, unspecified
- Q21.19 Other specified atrial septal defect
- Q21.2 Atrioventricular septal defectNon-billable
- Q21.20 Atrioventricular septal defect, unspecified as to partial or complete
- Q21.21 Partial atrioventricular septal defect
- Q21.22 Transitional atrioventricular septal defect
- Q21.23 Complete atrioventricular septal defect
- Q21.3 Tetralogy of Fallot
- Q21.4 Aortopulmonary septal defect
- Q21.8 Other congenital malformations of cardiac septa
- Q21.9 Congenital malformation of cardiac septum, unspecified
Clinical Terms in This Code Range
Definitions from the National Library of Medicine for conditions coded in the Q21 range.
Aortopulmonary Septal Defect
A developmental abnormality in which the spiral (aortopulmonary) septum failed to completely divide the TRUNCUS ARTERIOSUS into ASCENDING AORTA and PULMONARY ARTERY. This abnormal communication between the two major vessels usually lies above their respective valves (AORTIC VALVE; PULMONARY VALVE).
Double Outlet Right Ventricle
Incomplete transposition of the great vessels in which both the AORTA and the PULMONARY ARTERY arise from the RIGHT VENTRICLE. The only outlet of the LEFT VENTRICLE is a large ventricular septal defect (VENTRICULAR SEPTAL DEFECTS or VSD). The various subtypes are classified by the location of the septal defect, such as subaortic, subpulmonary, or noncommitted.
Endarteritis
Inflammation of the inner endothelial lining (TUNICA INTIMA) of an artery.
Tetralogy of Fallot
A combination of congenital heart defects consisting of four key features including VENTRICULAR SEPTAL DEFECTS; PULMONARY STENOSIS; RIGHT VENTRICULAR HYPERTROPHY; and a dextro-positioned AORTA. In this condition, blood from both ventricles (oxygen-rich and oxygen-poor) is pumped into the body often causing CYANOSIS.
Tunica Intima
The innermost layer of an artery or vein, made up of one layer of endothelial cells and supported by an internal elastic lamina.
About the Q21 Code Range
ICD-10 codes Q21 cover congenital malformations of the cardiac septa, which are defects in the heart's wall separating its chambers. These codes are essential for identifying specific types of septal defects present at birth.
The primary conditions classified under Q21 include ventricular septal defect (Q21.0), known also by terms like supracristal or perimembranous ventricular septal defect, which involve holes in the septum between the heart’s ventricles. Atrial septal defects (Q21.1 to Q21.19) represent gaps in the wall between atria and include types such as secundum atrial septal defect (ostium secundum), patent foramen ovale, and sinus venosus defects. The atrioventricular septal defects (Q21.2 series) involve abnormalities of the septum and valves between atria and ventricles and have synonyms like endocardial cushion defect. Complex defects like tetralogy of Fallot (Q21.3) combine several malformations. Aortopulmonary septal defect (Q21.4) and other rare malformations (Q21.8) are also coded here. The unspecified code Q21.9 is used when the precise defect isn’t clearly identified. These ICD-10 codes help healthcare providers accurately classify congenital septal heart defects for diagnosis, treatment, and documentation.
Questions About This Page
How many billable codes are in the Q21 range?
Of the 20 codes in this range, 17 are billable and valid for claim submission from October 1, 2025 through September 30, 2026. Category header codes group them but cannot be reported on claims.
What does the Q21 range classify?
The range classifies congenital malformations of cardiac septa. Each code links to its own reference page with billing status, MS-DRG grouping, coding notes, and clinical information.
Related References
Source: CMS FY 2026 ICD-10-CM Tabular List and order file, effective October 1, 2025 through September 30, 2026.
