ABSTRACT
A 6-year-old boy who had been found to have hypertrophic obstructive cardiomyopathy presented with severely limited symptoms of heart failure due to progressive left ventricular outflow obstruction. Cardiac catheterization revealed the peak systolic pressure gradient of 87mmHg at left ventricular outflow, and systolic anterior motion of the anterior mitral leaflet with concomitant mitral regurgitation was observed by echocardiography. Transaortic septal myectomy was performed using transesophageal echocardiography guidance before, during and after surgery. Although the patient needed permanent pacemaker implantation for postoperative complete heart block, the procedure reduced the left ventricular outflow obstruction and relieved his symptoms.