Penn electrophysiologist David J. Callans, MD, offers insights on what is perhaps the most difficult medical issue confronting clinicians who treat the arrhythmias: the use of anticoagulants. Dr. Callans discusses the nuances of anticoagulation across the spectrum of the arrhythmia population, discussing the peri-procedural parameters for starting and stopping these agents, bleeding and thromboembolic risks, and comparisons of warfarin and the new generation of blood thinning drugs.