We report the case of a 13-year-old girl with congenitally corrected transposition of the great arteries. Since the implantation of a conventional pacemaker for acquired complete atrioventricular block, the patient experienced increased heart failure symptoms. Using triplane tissue Doppler imaging, significant intraventricular dyssynchrony induced by unilateral pacing and associated with diminished exercise capacity was demonstrated. A biventricular pacemaker was successfully implanted transvenously, leading to synchronous activation of the systemic ventricle and improved exercise capacity.