Researchers at Baylor College of Medicine are conducting research on Wolff-Parkinson-White syndrome and are recruiting children and adults with this condition and their close relatives. The cause of sporadic WPW is mostly unknown. The purpose of this study is to help identify genes that are associated with WPW syndrome. Participants are asked to provide a small blood sample at the time of enrollment, and a brief medical history and family history for heart diseases/arrhythmia will be obtained. Participants will be compensated for expenses related to parking. The blood samples will be used to compare the genes in the affected individuals with their close relatives. Your participation in this study will help us understand the genetic basis of WPW syndrome.