Is there an over-the-counter treatment for Wolff-Parkinson-White syndrome?

No. This is an arrhythmia that is caused by an abnormal electrical connection between the top and bottom chambers of the heart. If it causes symptoms (chest pain, shortness of breath, fainting), you need to talk to an electrophysiologist (doctor that specializes in heart rhythm problems) who can perform an ablation that is usually curative.