A 66-year-old man underwent catheter ablation for Wolff-Parkinson-White syndrome. When we advanced the ablation catheter clockwise in the left ventricle, it was entrapped and became unable to control. Thus, the patient underwent open heart surgery for catheter removal. During the surgery, the last few millimeters of the catheter were observed entrapped by multiple basal chordae of the posterior mitral valve. We released the catheter safely, and visual inspection of the left ventricle showed no abnormalities. His postoperative course was uneventful. Ablation catheter entrapment in the heart is a rare but severe complication that requires open heart surgery.