Cardiovascular Center, Korea University Guro Hospital, Seoul, Korea. Division of Cardiology, Seoul St. Mary's Hospital, Seoul, Korea. Division of Cardiology, St. Paul's Hospital, Seoul, Korea. Division of Cardiology, Korea University Ansan Hospital, Ansan, Korea. Division of Cardiology, Korea University Anam Hospital, Seoul, Korea. Division of Cardiology, Maryknoll Medical Center, Busan, Korea. Cardiovascular Center, Seoul National University Hospital, Seoul, Korea. Valvular Heart Disease Center, Asan Medical Center Heart Institute, Seoul, Korea. Department of Cardiology, Seoul Medical Center, Seoul, Korea. Division of Cardiology, Severance Cardiovascular Hospital, Seoul, Korea. Division of Cardiology, Yeungnam University Medical Center, Daegu, Korea. Division of Cardiology, Ulsan University Hospital, Ulsan, Korea. Heart Center of Chonnam, National University Hospital, Gwangju, Korea. Division of Cardiology, Veterans Health Service Medical Center, Seoul, Korea. Division of Cardiology, Hanyang University Hospital, Seoul, Korea. Yuhan Research Institute, Yuhan Corporation, Yongin, Korea.