**2. Forms of aortic stenosis**

Subaortic stenosis (SAS) is common congenital cardiac defect in dogs [3, 4] and pigs [5]. In cats, SAS has not been so often described [1, 6–8].

Several classifications are used for aortic stenosis. According to anatomic location, aortic stenosis is classified into valvular (VAS), subvalvular (SAS), or supravalvular (SupAS) [9].

Based on functional characteristics of obstruction, subvalvular cases are further categorized as either fixed (static) or dynamic (labile) [2].

A dynamic form of subaortic stenosis can occur in the following instances: in a hypertrophied left ventricle (LVH) due to protrusion of the ventricular septum into the LVOT, systolic anterior movement of the anterior mitral valve leaflet (SAM) which occurs concurrently or in the absence of LVH, and in cases where aortoseptal angle is smaller than 180o [10].

The subvalvular form—subaortic stenosis (SAS)—has been reported as the most frequently seen (in 95%) and can be presented as a complete or incomplete ring [1, 2, 11–13].
