Rapid firing in a pulmonary vein (PV) with the spontaneous onset of atrial fibrillation (AFib). Two sinus beats are followed by a premature atrial complex (PAC) then rapid ectopy seen on a catheter positioned in a PV that starts AFib. Source: ATRIAL FIBRILLATION, ATRIAL FLUTTER, AND ATRIAL TACHYCARDIA, Hurst's The Heart, 14e Citation: Fuster V, Harrington RA, Narula J, Eapen ZJ. Hurst's The Heart, 14e; 2017 Available at: http://accessmedicine.mhmedical.com/DownloadImage.aspx?image=/data/books/2046/hurst14_ch83_f002.png&sec=176563715&BookID=2046&ChapterSecID=176563698&imagename= Accessed: March 02, 2018 Copyright © 2018 McGraw-Hill Education. All rights reserved