A 15-year-old boy who had been given an orthotopic heart transplant 12 years earlier underwent radiofrequency ablation after 14 months of tachycardia. At the time of the procedure, the patient presented moderate signs of heart failure and tachycardia-induced cardiomyopathy. During electroanatomical mapping we identified a focal atrial tachycardia with origin in the donor right atrium and bi-directional atrio-atrial conduction. After successful focal ablation the patient had two alternating atrial activation patterns, representing the recipient and the donor heart sinus rhythm. Two months after the ablation heart failure symptoms were in regress, and the patient was still in sinus rhythm.