Primarily, the degree of right ventricular outflow tract obstruction varies between patients and generally determines clinical symptoms and disease progression.Presumably, this arises from an unequal growth of the aorticopulmonary septum (aka pulmonary outflow septum). : 199  The aorta is too large, thus "overriding," and this "steals" from the pulmonary artery, which is therefore stenosed. This then prevents ventricular wall closure, therefore VSD, and this increases the pressures on the right side, and so the R ventricle becomes bigger to handle the work. : 199

Additional anomalies
In addition, tetralogy of Fallot may present with other anatomical anomalies, including:: 66–8 
stenosis of the left pulmonary artery, in 40%
a bicuspid pulmonary valve, in 60%
right-sided aortic arch, in 25%
coronary artery anomalies, in 10%
a patent foramen ovale or atrial septal defect, in which case the syndrome is sometimes called a pentalogy of Fallot
an atrioventricular septal defect
partially or totally anomalous pulmonary venous returnTetralogy of Fallot with pulmonary atresia (pseudotruncus arteriosus) is a severe variant in which there is complete obstruction (atresia) of the right ventricular outflow tract, causing an absence of the pulmonary trunk during embryonic development. : 67–8  In these individuals, blood shunts completely from the right ventricle to the left where it is pumped only through the aorta. The lungs are perfused via extensive collaterals from the systemic arteries, and sometimes also via the ductus arteriosus. : 67–8

Diagnosis
There are three different useful diagnostic tests used for the diagnosis of tetralogy of Fallot. These include a chest radiograph, electrocardiogram, and echocardiogram. The echocardiography determines the final diagnosis and typically offers enough information for surgical treatment planning.
Alternative horseshoeing methods
New non-invasive horseshoeing methods are available for farriers to take advantage of. They encapsulate the damaged hoof, protecting and supporting the sensitive internal structures. This prevents further deterioration, whilst also immediately reducing pain and improving the horse’s ability to move. The resulting comfort also reduces overall stress levels, leading to a faster recovery as the horse can quickly return to a regular routine. Aggressive therapies
Dorsal hoof wall resectionA dorsal hoof wall resection may help in certain conditions after consultation with an experienced veterinarian and farrier team. If decreased bloodflow distal to the coronary plexus is seen on a venogram, or when a laminar wedge forms between P3 and the hoof wall, preventing the proper reattachment (interdigitation) of the laminae, this procedure may be beneficial. When the coffin bone is pulled away from the hoof wall, the remaining laminae will tear. This may lead to abscesses within the hoof capsule that can be severe and very painful, as well as a mass of disorganized tissue called a laminar (or lamellar) wedge. Coronary groovingCoronary grooving involves removing a groove of hoof wall just distal to the coronary band. It is thought to encourage dorsal hoof wall growth and improve alignment of the wall. Deep digital flexor tenotomy
Because the rotation of P3 is exacerbated by continued pull on the deep digital flexor tendon, one approach to therapy has been to cut this tendon, either in the cannon region (mid-metacarpus) or in the pastern region.