1. From the Arrhythmia Service (D.H.B., P.B.N), Cardiac Research and Methods Center (G.A.W.), and the National Cardiac PET Centre, Division of Cardiology, Department of Medicine (B.A.M., R.K., R.A.d.K., J.R., J.D., R.S.B.), University of Ottawa Heart Institute; and the Division of Nuclear Medicine, Department of Medicine, The Ottawa Hospital and University of Ottawa (E.L.), Ottawa, Ontario, Canada.