ABSTRACT
Malformations of cardiac valves and their adjacent or support structures are common, especially in dogs. Defects that involve the semilunar valve regions mainly cause ventricular outflow obstruction, although mild, and usually inaudible, valvular regurgitation commonly coexists. Outflow obstructive lesions can occur at the semilunar valve itself, just below the valve, or in the proximal great vessel. Severe defects are relatively straightforward to identify. The facts that some animals have a soft murmur without structural disease and that certain mild defects might not cause an audible murmur are confounding factors. Ventricular outflow obstruction, whether caused by a fixed stenotic lesion or muscular obstruction during systole, imposes a systolic pressure overload on the affected ventricle. The high pressure generated within the ventricle serves as a source of potential energy, which is converted to kinetic energy as red cells accelerate and are rapidly ejected across the stenosis.
