An 84-year-old woman with type B WPW with Ebstein anomaly was admitted with heart failure. She had rapid wide QRS tachcardia due to accessory pathway conduction associated with atrial fibrillation (AF). Since transesophageal echocardiography before catheter ablation showed a left atrial thrombus, ablation was performed using a 3D mapping system under AF. After marking the functional tricuspid anulus with intracardiac echocardiography, three dimensional intracardiac electrogram visualization (ripple map) during AF enabled clear identification of location of the accessory pathway. After ablation, there was no complication of cerebral infarction and heart failure improved.