A 49-year-old woman with dextrocardia and situs inversus underwent catheter ablation of paroxysmal atrial fibrillation (AF). During the electrophysiologic study, AF triggered by frequent premature atrial contractions (PACs) with a short coupling interval exhibiting a "P on T" pattern occurred. Pulmonary vein mapping revealed that those PACs originated from right-sided (anatomic left) or left-sided (anatomic right) pulmonary veins. In this case with mirror-image dextrocardia, the P-wave morphologies in leads I and aVL and the II/III ratio of the P-wave amplitude were helpful for predicting a right- or left-sided pulmonary vein origin. © 2009, Wiley Periodicals, Inc.