Development of dilated cardiomyopathy in patients with congenital complete atrioventricular block with or without pacemaker is well described. We report a case of dilated cardiomyopathy in a child with congenital complete atrioventricular block, long-QT syndrome, and VVI pacemaker. Temporary pacing in the right ventricular outflow tract demonstrated a 63% increase in cardiac output. After change to biventricular DDD pacing, left ventricular systolic function and diastolic dimensions normalised.