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The term 'stenosis' refers to any forms of narrowing of tubular body sections such as blood vessels or other hollow organs with quite different causes and symptoms in medicine.

In the heart, stenoses are mainly found on the semilunar valve, i.e. on the aortic valve and on the pulmonary valve. Rarely affected are the atrioventricular valves, i.e. mitral and tricuspid valve.

Pulmonary stenosis is, as the name implies, a stenosis – that is, narrowing the pulmonary artery. It is the second most frequent congenital hereditary disease in the dog and is already completely present at birth. The pulmonary stenosis can occur individually or in combination at three places:

• just below the pulmonary valve (subvalvular)
• on the pulmonary valve itself (valvular), the most common form
• above the pulmonary valve (supravalvular)

The pulmonary stenosis is the most common due to a missed (thickened and adhered) pulmonary valve. As a result of the constriction, the blood must therefore be pumped against a resistance. The heart muscle must apply correspondingly more force in order to carry the blood out of the heart into the pulmonary circulation. The increased pressure leads to a higher blood flow velocity and to turbulences, which can be perceived as heart sounds during auscultation. Depending on the severity of the pulmonary stenosis, thickening of the muscles occurs and a regular flow through the heart is more difficult or impossible, which leads to an oxygen under-supply. In many cases pulmonary stenosis is accompanied by pulmonary insufficiency. Cardiac arrhythmia can also develop, especially in the case of high-grade pulmonary stenosis.

(hand drawn, based loosely on http://www.transplantation-verstehen.de/dotAsset/25070.jpg)

The aortic stenosis is, as the name implies, a stenosis – which is narrowing the aorta. It is the most common congenital hereditary disease in Germany, but it does not have to be fully present at the time of birth, but can still vary slightly thereafter. The aortic stenosis can occur individually or in combination in three places:

• just below the aortic valve (subaortic stenosis), most common form, congenital
• on the aortic valve itself (valvular aortic stenosis), congenital or acquired
• above the aortic valve (supravalvular aortic stenosis), very rare

Most frequently the so-called sub-aortic stenosis occurs with constriction in the left ventricular chamber below the aortic valve, which is why we refer in the following chapters mainly to this form of aortic stenosis. It is one of the most frequent congenital diseases in the dog. There are also three forms of subaortic stenosis:

• fibrous ring stenosis
• muscular stenosis
• combination of fibrous ring stenosis and muscular stenosis

As a result of the constriction, the blood must therefore be pumped against a resistance. The heart muscle must apply correspondingly more force in order to carry the blood out of the left heart chamber into the main artery (aorta). The increased pressure leads to a higher blood flow velocity and to turbulences, which can be perceived as heart sounds during auscultation. Depending on the severity of the aortic stenosis, thickening of the musculature occurs and a regular flow through the heart is more difficult or impossible, which leads to an oxygen under-supply. In many cases, aortic stenosis is combined with aortic insufficiency.

(hand drawn, based loosely on http://www.transplantation-verstehen.de/dotAsset/25070.jpg)