Cardiology Coding Alert

Question: I am reviewing a pediatric inpatient chart. The patient has a confirmed diagnosis of tetralogy of Fallot (TOF), a congenital heart defect that includes pulmonary stenosis, ventricular septal defect (VSD), overriding aorta, and right ventricular hypertrophy. The provider documents the diagnosis in the history and physical and confirms that the patient has not yet undergone surgical repair. What ICD-10-CM code should I use to report this?

New York Subscriber

Answer: The correct code is Q21.3 (Tetralogy of Fallot), and here’s why.

First, recognize that tetralogy of Fallot is a specific congenital heart defect and not a general heart condition. The key components — pulmonary stenosis, ventricular septal defect, overriding aorta, and right ventricular hypertrophy — are all intrinsic to the TOF diagnosis. You do not code each component separately because ICD-10-CM provides a combination code for the syndrome.

ICD-10-CM code Q21.3 is the standard diagnosis code used for TOF, regardless of whether the patient has undergone repair. According to the ICD-10-CM 2026 Official Guidelines, you should code the congenital condition as documented.

Watch out: You should not use Q21.9 (Congenital malformation of cardiac septum, unspecified), because this code is for unspecified congenital heart malformations. If TOF is documented, this code is too vague.

You should also not use I51.9 (Heart disease, unspecified), because this diagnosis code is used for unspecified heart disease in adults; congenital defects should not be coded here.

Also, avoid a diagnosis from the Q25.4- (Other congenital malformation of aorta) category, because these codes are specific to pulmonary stenosis, which is only one component of TOF. Using this code alone would be incomplete and inaccurate.

Additional tips:

• Always check the patient’s history for any prior surgical repair or palliation. Postsurgical codes may require additional coding for sequelae or complications.
• For congenital heart defects, ICD-10-CM classifies the condition by type of defect, so you should code the most specific syndrome rather than individual components unless documentation specifies otherwise.
• Remember that congenital heart defects are reported regardless of age if they are present and clinically relevant.

Suzanne Burmeister, BA, MPhil, Medical Writer and Editor