Atrial flutter in donor part of orthotopic heart transplant has been reported and treated by radiofrequency ablation in the past. Complex fractionated atrial electrogram (CFE) mapping has been used to simplify the ablation of chronic atrial fibrillation. Here, we report a case with atrial flutter in an orthotopic heart transplant whose circuit mapping was difficult. Using CFE helped us to define the arrhythmia circuit easily and perform curative ablation.