In tetralogy of fallot, you have both a stenotic pulmonary valve AND an overriding aorta. The underlying problem can be thought of as the AP septum forming unevenly, making the pulmonary trunk (PT) too narrow, and the Aorta too wide. Since the septum isn't in the midline, it doesn't join with the muscular part of the ventricular septum, and you have an overriding aorta creating a VSD. This would create a left to right shunt, until eisenmenger's syndrome kicks in.
The RVH would happen because of pulmonic stenosis and the increased blood volume due to the VSD.
I hope that answered your question?
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