Cyanotic heart disease due to a hypoplastic right ventricle with pulmonary valve atresia, an intact ventricular septum, with atrial level shunting in a day‐old Arabian foal

An 8‐h‐old Arabian foal was presented for evaluation of progressive weakness since birth. The foal presented laterally recumbent with pale and muddy mucous membranes, a grade III/VI left basilar murmur, and an irregularly, irregular rhythm. Transthoracic echocardiogram along with an electrocardiogram (EKG) was performed. Atrial fibrillation was recorded throughout the examination. The left and right atria were both significantly enlarged. A right to left shunt across the atrial septum was confirmed via an intravenous injection of agitated saline. The tricuspid valve was rudimentary without apparent atrioventricular flow and no ventricular septal defect was appreciated. The animal was euthanased, and necropsy found dysplasia of the tricuspid valve, a hypoplastic right ventricle with pulmonary valve atresia, and an intact ventricular septum. This condition is similar, both haemodynamically and in terms of prognosis, to tricuspid atresia, which has been described previously in Arabian foals, with the exception that there is the complete absence of connection between the atrium and ventricle in the case of tricuspid atresia. Of 14 previously reported cases of tricuspid atresia in neonatal foals, nine were Arabian foals. Further investigation into the possibility of hypoplastic right ventricle as a familial condition in the Arabian breed should be considered.