Tetralogy of Fallot (TOF) is the commonest cyanotic congenital heart disease (CHD), with an incidence of 3 in 10,000 births, representing 10% of all CHDs. Whilst there is a spectrum of presentations and morphological variants, the classical description comprises a non-restrictive ventricular septal defect (VSD), an over-riding aorta, right ventricular outflow tract obstruction (RVOTO) with resultant right ventricular hypertrophy. Presentation is usually cyanosis and murmur in the neonatal period, although it can present later in milder forms.

Associations with chromosomal abnormalities are described, with microdeletion of 22q11.2 (cf. DiGeorge and velocardiofacial syndromes) being most frequent and trisomy 21, 13 and 18 also being overrepresented.

A hypercyanotic (‘tet’) spell is the feared complication of an unrepaired TOF, caused by excessive shunting, with potential lethal consequences. There is an excellent prognosis following surgical repair and most are asymptomatic. Despite this, there is excess mortality and morbidity due to chronic pulmonary regurgitation, recurrence of pulmonary stenosis, RV dysfunction, ventricular arrhythmias and sudden cardiac death.