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ii Aortic stenosis (AS) is a common, heritable congenital heart defect affecting Boxer dogs. Severely affected dogs are at risk for heart failure, endocarditis, and sudden death. Veterinarians usually screen for AS through auscultation. When a typical murmur is auscultated, an echocardiogram is performed to identify the presence and severity of the cardiac defect. In the setting of a soft murmur, echocardiographic imaging lesions are often absent, and a noninvasive diagnosis is based on Doppler-identification of high velocity flow across the left ventricular outflow tract (LVOT). However, similar increases in LVOT velocity can occur in normal dogs under sympathetic stimulation. This distinction between mild AS and normal variation is pivotal to Boxer breeders. In a review of 201 healthy adult boxers, over 50 % had left basilar ejection murmurs typical of AS, and the combination of a murmur and elevated LVOT velocity was seen in 36%. For those dogs, the presence of a murmu