A 13-year-old boy with hypertrophic obstructive cardiomyopathy was treated with dual-chamber pacing after severe progression of left ventricular outflow tract obstruction and of clinical symptoms despite drug therapy. Rapid intrinsic atrioventricular conduction was overcome and complete preexcitation of the septum achieved by omitting atrial sensing and programming constant atrial pacing with a short atrioventricular delay of 70 msec. After 8 weeks of therapy, a reduction of the left ventricular outflow tract gradient from 125 to 16 mmHg and remodeling of the left ventricle were demonstrated.