This patient’s EKGs had been read as left bundle branch block repeatedly, but the correct diagnosis is WPW. There is a short PR interval and delta waves (best seen in the limb leads) that would not be explained by a block, but rather by pre-excitation through an accessory pathway. The left bundle branch morphology of the QRS is caused by the location of the accessory pathway, which is on the right. Depolarization begins on the right side of the heart and then swings across to the left, as it would in LBBB.