Tricuspid atresia may be defined as congenital absence or agenesis of the tricuspid valve. It is the third most common cyanotic congenital heart defect; the other two more frequently observed cyanotic congenital cardiac anomalies are transposition of the great arteries and tetralogy of Fallot. Tricuspid atresia is the most common cause of cyanosis with left ventricular hypertrophy.

Electrocardiographic findings are virtually diagnostic of tricuspid atresia in a young patient with congenital heart disease. The electrocardiogram demonstrates right atrial hypertrophy, an abnormal superiorly oriented major QRS vector, the so-called left axis deviation.