ICD-10-CM 2027
ICD-10 code for Fallot's syndrome
From the official ICD-10-CM alphabetic index entry “Syndrome › Fallot's”. Page updated September 29, 2026.
About coding Fallot's syndrome
The ICD-10-CM code for Fallot's syndrome is Q21.3 (Tetralogy of Fallot).
Within Q21 (congenital malformations of cardiac septa), Q21.3 is specifically for tetralogy of Fallot. Related codes cover ventricular septal defect (Q21.0), atrial septal defect (Q21.1), atrioventricular septal defect (Q21.2), Aortopulmonary septal defect (Q21.4), other congenital malformations of cardiac septa (Q21.8) and congenital malformation of cardiac septum, unspecified (Q21.9).
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 306 (Cardiac Congenital and Valvular Disorders with MCC, relative weight 1.546) and DRG 307 (Cardiac Congenital and Valvular Disorders without MCC, relative weight 0.9148), in MDC 05 (Diseases and Disorders of the Circulatory System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
Common questions about Fallot's syndrome ICD-10 codes
What is the ICD-10 code for Fallot's syndrome?
- Q21.3 — Tetralogy of Fallot.
Is Q21.3 billable?
- Yes. Q21.3 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can Q21.3 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict Q21.3 as a principal diagnosis.
Is Q21.3 a CC or MCC?
- Q21.3 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.