Sub-Aortic Stenosis (SAS): common congenital heart disease in Boxers and other large breed brachycephalic dogs. The puppies are born with an obstacle to the normal flowing across the aortic valve. In the most severe cases, the heart has to make much bigger effort to pump the blood out in the circulation because of this obstruction. As consequence, the heart muscle thickens and "eventually this interferes with the pumping chamber´s flexibility and ability to fill". At this point, arrhythmias are also often present.