An 80-year-old man underwent catheter ablation for atrial tachycardia (AT), which developed after catheter ablation for atrial fibrillation. The AT was diagnosed as dual-loop tachycardia, which included peri-mitral and roof-dependent ATs. An ethanol infusion into the vein of Marshall resulted in left phrenic nerve paralysis. During the procedure, the phrenic nerve paralysis was completely relieved.