Subaortic stenosis produced by an accessory mitral valve: the role of echocardiography.

Subaortic stenosis caused by an accessory mitral valve is an exceedingly rare finding. We report the case of an asymptomatic 14-year-old patient, in whom transthoracic echocardiography revealed an accessory mitral valve in the left ventricular outflow tract, producing mild subaortic stenosis. Except for an aneurysm of the interventricular septum, with no shunt, there were no other anomalies. Transesophageal echocardiography provided details about the morphology and location of the accessory valve. Being asymptomatic and having only a mild gradient, antibiotic prophylaxis for infective endocarditis and follow-up were recommended. After 2 years the patient is asymptomatic, with a similar echocardiographic gradient.