Dynamic obstruction of the left ventricular outflow tract in four young dogs.

Four young dogs presented for evaluation of left-sided systolic heart murmurs all showed echocardiographic changes consistent with dynamic left ventricular outflow tract (LVOT) obstruction and subjective evidence of concentric left ventricular hypertrophy. In three of the dogs, abnormal mitral valve apparatus and systolic anterior motion of the anterior mitral valve leaflet with associated mitral insufficiency were also detected. All dogs were medicated with a beta1-adrenergic antagonist. Subsequent examinations showed that the dynamic LVOT obstruction and left ventricular concentric hypertrophy had almost completely resolved. Dynamic LVOT obstruction is a rare condition of young dogs of different breeds. The precise aetiology of the condition remains uncertain. Whether resolution of the outflow obstruction in these four cases was a consequence of treatment or due to changes in ventricular architecture brought about by ageing cannot be established.